History of Trespass
Under traditional common law principles, there were effectively four categories of persons who could enter an occupier’s premises. The first were ‘contractors’, who were owed the highest duty of care, namely to ensure that the premises were fit for the purposes of the contract. Secondy, ‘invitees’ were owed a lower duty of care, the occupier being under a duty to take reasonable steps to ensure that the invitee is not harms by any unusual danger on the premises. Thirdly, there were ‘licensees’, who were there by express or implied permission. The duty owed to licensees was to provide that they are not harmed by any concealed danger on the property. Lastly, there were trespassers, persons who were present on the occupier’s premises without permission, express or implied. Trespassers were owed a comparatively low duty of care: to avoid deliberately or recklessly causing them harm.
The legal landscape was altered by the Occupiers Liability Act 1957, which amalgamated the first three categories into one: ‘visitors’. Under s.2 (2) of the 1957 Act, the duty owed to visitors is essentially to take ‘such care as is reasonable in the circumstances to see that the visitor will be reasonable safe in using the premises for the purposes for which he is invited or permitted by the occupier to be there.’ Despite this change in the law, it wasn’t until the Occupiers Liability Act 1984 that the position vis-à-vis trespassers was reformed.
Occupier’s Liability Act 1984
The first question which must be asked in relation to trespassers is whether or not there is in fact a duty towards them in the circumstances. This issue is governed by s.1 (3) of the 1984 act. Three conditions must be satisfied, namely that the occupier is aware or has reasonable grounds to believe that a danger exists, he knows or has reasonable grounds to believe that the trespasser is in or may come into the vicinity of the danger, and the risk is one from which he is reasonably expected to offer some protection.
Moreover, if such a duty is established under s.1 (3), the issue then moves to the degree of protection the occupier is expected to provide. The duty is to provide such care as is reasonable in all the circumstances of the case to ensure that the trespasser does not suffer injury on the premises by reason of the danger concerned.
Section 1 (5) relates to the extent to which such a duty may be discharged by taking such steps as are reasonable in the circumstances to give warning or to discourage persons from incurring risk, and s.1 (6) provides that no one is owed a duty of care in respect of risks willingly accepted as his by the person incurring the risk.
It is now helpful to consider the workings of this legislation by reference to the main authority on the matter: Tomlinson v Congleton Borough Council  1 A.C 46
Facts of Tomlinson
This case relates to a lake that had been formed from a disused quarry by filling it with water, thus creating effectively an artificial beach area. Swimming was, however, prohibited in the lake, with the local authority displaying several ‘no swimming’ warning signs, and handing out leaflets advising of the dangers of swimming in the lake. The local authority was aware that, despite the warnings, people were generally paying no heed to the prohibition. On a particularly hot summer’s day, the Plaintiff, John Tomlinson, went swimming in the lake and, from a standing position in the water, dived into it. However, he grossly misjudged the depth of the water and struck his head against the bed of the lake, thus breaking his neck and suffering severe injuries which left him paralysed from the neck down. He sued the local authority on the basis that the accident was caused by the breach of the duty of care they owed him as a trespasser under the Occupier’s Liability Act 1984. The case eventually reached the House of Lords in 2004, who made an authoritative ruling on the matter.
How the Act functions in practice
a) The distinction between visitor and trespasser
Despite the two categories of persons being governed by two separate pieces of legislation, it is not always clear into what category a certain person doing a certain activity may fall. In fact, the categories are in many ways transient, in that a person can go from a visitor on certain premises to a trespasser depending on what activity he chooses to perform on the said premises. For example, in Tomlinson, persons on the premises for the legitimate purposes of sunbathing etc. would be classed as visitors. John Tomlinson would have been classed as a visitor himself. However, once he had chosen to ignore the warning signs and engage in an activity which was not permitted by the owners of the lake, he ceased to be a visitor and assumed the title of trespasser, thus altering the legal duty owed to him. This position is humorously summed up by Scrutton LJ in The Carlgarth case: “when you invite a person into your house to use your staircase, you do not invite him to slide down the banisters.”
b) Scope of the duty under the 1984 Act
To come within the scope of the 1984 Act the danger must be ‘due to the state of the premises or to things done or omitted to be done on them.’ The key distinction here is between an activity carried out on a premises which carried with it an inherent danger, and a premises which is in a dangerous state. This point can be illustrated again using the Tomlinson case. There was nothing about the lake which made it any more dangerous than any other lake. There was nothing particularly dangerous in it, nor any hidden dangers that one might not be able to see at first blush. Obviously, due to its inherent characteristics it had the potential to be life threatening in that a person could drown in it or suffer injury by diving into it, but any injury caused would not be because the lake was in a ‘dangerous state’. Mr Tomlinson dived into the lake at a shallow area, therefore suffering injury because he chose to engage in an activity with inherent dangers, not because the premises were in a dangerous state. Therefore, in order for the premises to be classed as ‘in a dangerous state’, it would appear that there must be some unusual danger on the premise. This was well illustrated by Lord Hoffman in Tomlinson in observing that if someone decides to go mountaineering he runs the risk of potentially stumbling or misjudging where to put his weight. However, any risk involved would not be due to the state of the premises, but rather the activity the mountaineer chose to perform thereon.
If the danger is not due to the state of the premises, it must otherwise be due to ‘things done or omitted to be done’ on the premises, to give rise to a duty under the 1984 Act. In Tomlinson, it was held that the mere fact of not preventing people from swimming in the lake does not give rise to a duty to prevent people swimming in the lake. This was seen as illogical. An example of what would qualify as a sufficient omission would be a failure to alert swimmers to the presence of water skis on the lake. To qualify, the act or omission must be an activity or lack of precaution which causes risk.
c) Nature of the duty
Section 1 (3) of the 1984 Act has three conditions which must be satisfied. The occupier must have knowledge or foresight of the danger, he must have knowledge or foresight of the trespasser, and it must be reasonable for the trespasser to protect some protection in the circumstances. In Tomlinson, the Court found that the fact that the local authority were aware that there had previously been swimming accidents at the lake meant that they did have knowledge of the danger. Moreover, they had knowledge or foresight of the trespasser, as they knew that the lake was regularly frequented by swimmers, despite their efforts to prevent this. The crucial question was therefore whether or not it was reasonable to expect protection. This question raises some interesting points about this area of law.
The House of Lords engaged in a risk versus social benefit style analysis of the situation. First, they looked at the exact risk involved, and concluded that no duty is involved where the risk is perfectly obvious. This followed Darby v The National Trust  PIQR 372 where a man had drowned swimming in a pond where the National Trust had failed to make it clear that swimming was not permitted. Despite this, the court were of the opinion that no duty could arise in the circumstances because the risk from drowning in a pond was perfectly obvious. This was echoed in Tomlinson, where Lord Hoffman agreed that the risk was obvious and would not have required the local authority to take any steps to warn John Tomlinson of the obvious danger.
Moreover, the court considered that in some cases, the risk may be so slight, and the social benefit of the activity so great, that it would not be unreasonable to fail to take measures to prevent the occurrence of the risk even though it was foreseeable. For example, in Bolton v Stone  AC 850 a woman was seriously injured while standing outside her front door when she was struck by a cricket ball which flew out from a neighbouring cricket ground as it had been ‘hit for six’. The consequences of a finding of liability would have been that the ground would no longer be able to be used for its socially useful purpose. Compared with the risk involved of someone being hit by a ball, which was vastly improbable, it was held that it was not negligent of the cricket club to fail to take measures to prevent the risk occurring.
To further illustrate this point one can use the analogy of a person walking along side a picturesque country river. Obviously, while walking alongside a river, there will always be the risk, albeit small, that you could slip and fall in, or a gust of wind could knock you off your stride and cause you to fall in. This is obviously extremely unlikely, but nonetheless possible. In such circumstances, despite the foreseeable risk, it would not be reasonable to expect that the river be fenced off to prevent such a risk occurring. The benefit to be gained from the world being able to walk alongside and look at a river is seen to outweigh the minimal risk of someone falling in. In this respect, there is a risk versus benefit analysis involved in any case involving a social activity and an injury to a trespasser. In Tomlinson, the risk of someone injuring themselves while diving may have existed, but would it have been reasonable to close off the beach area, thus preventing the vast majority of its users from being able to engage in permitted activities thereon? While not an issue in the case, Lord Hoffman’s general tenor suggested it would not have been.
Occupier’s liability to trespassers is an area of law which is largely governed by common sense. If a danger is perfectly obvious, it may not be reasonable to have to take measures to prevent it. If a danger is hidden or secret, then a duty to warn of take preventative measures will arise under the Act. What type of protection to expect is dependent on the nature of the risk. It is not reasonable to prevent injury occurring from a 60,000watt power station by erecting a mere warning sign beside it, similar as it is not reasonable to fence off an entire lake just because of the risk someone might fall into it. It is a question of individual autonomy against reasonable expectations of protection, designed by the law to ensure that while life is accompanied with some protection against risk, some element of risk still exists to allow people to live.