Disclaimer Notices

Nah. It would be of no relevant legal effect.

But, the general principles of negligence and specifically the Occupier's Liability Act 1995 would apply. Quick run through - this is not legal advice :-

Broadly, a person exercising such control over a premises (land, water, any structures, vehicles, vessels, aircraft, trains) that it is reasonable to impose on that person a duty of care towards an entrant on the premises is an occupier.

A 'recreational user' is a person who, with or without the occupier's permission, or at the occupier's implied invitation, is present on the premises without a charge.

A 'visitor' is aperson who is present on the premises at the invitation of or with the permission of the occupier or pursuant to a contract (i.e. pays a charge) or has a right to be present on the premises.

Re visitors - the occupier has to take such care as is reasonable in all the circumstances towards the visitor, having regard to the care which the visitor should take for their own safety. (note there is potential for the occupier to restrict his/her duty of care to visitors by displaying a notice specifically warning that the visitor is on a premises and stating the nature of the potential danger in such a way as allows the visitor to avoid the danger).

Re recreational users - the occupier owes a duty not to intentionally injury the person or damage their property, and not to act with reckless disregard for the person or property of the occupier. Whether you acted with reckless disregard is considered in light of whether the occupier knew or should have known there was a danger, whether the occupier knew or should have known that a person was likely to be on the premises, whether the danger was one which the occupier could be expected to have provided protection, how difficult it would have been to protect against the danger, the nature of the premises and some other stuff I can't remember.

Included in those factors is the nature of any warning given by way of sign or otherwise.

Specifically re structures, if you provide a structure for use by recreational users you have a duty to maintain it in a safe condition.

Now specifically about your query :-

...the locals would need the permission of the occupier of the land to erect the bench for a start or its a trespass.

Once it is there, the occupier has to maintain it in a safe condition.

If it's in a safe condition it is not a danger to anyone.

Your main hurdle here is probably getting permission to erect the bench in the first instance (I am presuming you have to deal with a local authority) and then you/they working out how it will be maintained.

You can't sue anyone (successfully) just because you fell off of a bench, presuming the bench & surrounds is in safe condition.