Hi Flipflopper
I was/am in a similar situation: I live in a modern housing estate where the builders moved off site 3 years ago. They are probably the beneficiaries of the site. My deeds also said about not keeping any poultry or livestock on the premises. I did a lot of searching online and the consensus of opinion, including from lawyers, was:
1. Seek the approval of your neighbours: reassure them you'll be right on top of any smells and rodents, and offer them eggs whenever possible
2. Keep the hens in good conditions, that way there will be no room for complaint from any neighbour and no need for them to call someone in from the council, SSPCA or other animal welfare agency, to check on the hens.
In other words: keep your nose (and hen run) clean!
My neighbour works in the council HQ, and she was telling me her boss has got hens in his garden (on another modern housing estate) - apparently the care of hens in the garden comes under Trading Standards and it's they who would deal with any complaint from the neighbours about noise, smell, infestations etc.
The chances of the builder and beneficiary of the land (especially in your case given that the developer has retired) coming along to see that everyone whose house he built is sticking to the terms of the deeds (and remember, these deeds prohibit things like the erection of satellite dishes on the front of the house, keeping a caravan in the drive-way, keeping a rabbit in a hutch in the garden
...) are pretty non-existent.
I got my hens a couple of weeks ago and *touch wood*, having got the neighbours' blessing and had them round to see the girls, it's just terrific fun (and that's without any eggs yet)
Go for it - you'll be a convert like everyone else is