Check with your local council before adopting hens. Some properties have covenants forbidding the keeping of hens due to their classification as livestock.
However The Allotments Act 1950, Chapter 31, Section 12 states that regardless of clauses in leases / tenancies / covenants / contracts or agreements to the contrary, the occupier of any land can keep hens and rabbits on it, for their own use, so long as they set up and maintain adequate housing and so long as they make sure that the hens / rabbits don’t become a nuisance or pose a threat to health.
Here is the exact wording:
Abolition of contractual restrictions on keeping hens and rabbits
(1) Notwithstanding any provision to the contrary in any lease or tenancy or in any covenant, contract or undertaking relating to the use to be made of any land, it shall be lawful for the occupier of any land to keep, otherwise than by way of trade or business, hens or rabbits in any place on the land and to erect or place and maintain such buildings or structures on the land as reasonably necessary for that purpose.
Provided that nothing in this subsection shall authorise any hens or rabbits to be kept in such a place or in such a manner as to be prejudicial to health or a nuisance or affect the operation of any enactment.
It should be noted that “the Allotments Act 1950 (and any other Act of Parliament) overrides all other sources of law, apart from European Directives”.