For the price range your looking at (£300-£400) have you thought about picking up a used camera, there are some bargins out there.
The link below is for a camera on e-bay, selling with a EF-S 55-250 MM f/4-5.6 IS lens which I would say is the minium you would need for taking pictures of birds.
Canon EOS Kiss 4 / 550D 18.0 MP Digital SLR Camera - Black (Kit w/ 18-55mm... (8714574549965) | eBay
happy shopping...