i think people will have a vested interest in looking after their own chickens so maybe you're worrying unnecessarily. also, your local council will have guidelines, i know mine do. however, it's wise to vet a person's ability to husband their livestock to a decent standard; in this respect you might like to stress the time and effort it takes to keep chickens before someone gets them.
perversely, my council deemed my run too big for my chickens and wanted them in a very small area. i can't see why they were so adamant on this point as more space meant happier chickens. i had approx 24 square metres though the council wanted a mere 7.
rules concerning poultry are to be found in Detail to Rules 7[1].2 and 7.3 of my authorities allotment rules:
HOUSING OF HENS - EXTERNAL
a) The minimum external floor space per bird will be 2 sq ft to a maximum total floor area of 24 sq ft i.e. shed and external run will not cover more than 72 sq ft.
f) Hens should have continuous daytime access to open air runs, these runs should be moved regularly to avoid fowl sick or muddy conditions which could lead to ill health or discomfort of the birds.
g) Precautions should be taken to protect the birds from and avoid disturbances by foxes, rodents and other animals.
h) There should be care not to leave any type of material on a plot which may attract rodents.
i) A tenant must ensure that the hens do not cause a nuisance to other plotholders or to local residents.
HEALTH
It cannot be too strongly emphasised that birds kept under any system can be prone to stress, injury and disease if management and husbandry are not of a high standard. The tenant must inspect the birds at least once daily and injured or dead birds should be removed promptly. Dead birds will be disposed of off site.
Ailing birds, and any birds suffering from injury such as open wounds or fractures, or prolapse of the vent should be segregated and treated, or if necessary, be humanely killed without delay.
Land on which birds are kept for prolonged periods may become ‘fowl sick’, i.e. contaminated with organisms which cause or carry disease to an extent which should seriously prejudice the health of poultry on the land.
Important indications of health are alertness, clear bright eyes, good posture, vigorous movements if unduly disturbed, active feeding and drinking, and clean, healthy skin, shanks and feet. Attention should be paid to any departure from the normal.
Apart from diet and hygiene, birds have other basic needs to keep them in a healthy condition. These are: freedom to turn round without difficulty, groom themselves, get up and sit down, rest undisturbed, stretch their legs and body, and perform wing flapping and dust bathing behaviour as well as to fulfil other health and welfare needs.
The early signs of ill health may include changes in food and water intake, in preening, in ‘chatter’ and in activity. In laying birds there may also be a drop in egg production, and changes in egg quality such as shell defects.
The City Council reserves the right not to allow fowl on any allotment plot.
Dead birds must now be disposed of according to the Animal By-Products Regulations 2003 – the only disposal route is (as Category 2 – waste) to an approved incineration or rendering plant. This aspect has an important implication for small scale poultry keepers, who cannot take any dead animal to a larger keeper, for example, for approved disposal unless they were themselves a registered Environment Agency Waste Carrier.
A recent amendment to The Welfare of Animals (Slaugher or Killing) Regulations 1995 is that where poultry are slaughtered for the food of Muslims or Jews, this can now only be undertaken by a licenced slaughterman in a licenced slaughterhouse.