Hi,
God that poor poor cat. I would prefer to think he/she is a stray, I can't bear to think that someone would let their cat get like that. Needs veterinrary treatment, Im sure the blue cross or PDSA would help you out. As someone else suggested don't involve the RSPCA as they don't like hard work and will almost certainly put the cat down
Looks quite Maine coon like or very damn near. I really hope you manage to get he/she sorted out, it must be so uncomfortable bless it. Try and avoid the ham, basic cat food is needed and just drinking water.
Keep us posted and well done for helping Beastie out, I imagine with a bit of work this could be "Beauty" instead
Izzie