Some links to some useful websites...

Cats

Feline Advisory Bureau

National (UK) Animal Welfare Charities

Cats Protection
National Canine Defence League (NCDL)
Royal Society For The Prevention Of Cruelty To Animals (RSPCA)

Local Animal Welfare Charities

Thornberry Animal Sanctuary

Sheffield

Sheffield City Council
Sheffield Forum (more specifically the pet owners forum)
Voluntary Action Sheffield

General Interest

BBC South Yorkshire Feature About The Shelter