Hi Vickster, welcome to birdforum. :hi:
The best thing you can do for this bird is to take it to a wildlife rehab centre. They can give it expert care which it will probably need for a few weeks. Cats carry a bacteria (Pasteurella multocida) in their saliva that is very toxic to birds and can cause death. Any bird found with a cat should be examined by a Wildlife Rehabilitator immediately.
Here is one in Leeds:
Wildlife Rescue, John Abbott, 62 King Edward Avenue, Horsforth, LEEDS, LS18 4BG 01532 587780 (birds and small animals)
If you don't have any luck there, then try these people: ALL SICK OR INJURED BIRDS & ANIMALS, CALL TIGGYWINKLES ON 01844 292 292
This advice is from Tiggywinkles Wildlife Hospital:
Pigeons and Doves
Baby pigeons and doves are different from all other British birds in that they are reared on a milky substance produced in their parents' throats. To rear them we use Tropican for very tiny pigeon, and ground corn mixed with water for larger birds. This mixture is then syringed straight into the pigeons crop. This should only be attempted by very experienced bird handlers.
Good luck with finding help, please let us know how you get on.
:t: