For anyone wanting to get the RSPCA involved, I'd think again, they have an appalling record for swiftly bumping off animals they've 'rescued'.
Re Catteries, there are good, bad and moderate, like most things, so seek local advice. Our latest cat doesn't like other cats, but he's been to stay in Catteries, and no reported problems. I think they recognise they've been put in 'barracks', have to lump it for a while, and they are in individual pens or cubicles (NB Someone mentioned 'runs' -- not all Catteries have them, or possibly as an optional 'extra').
And yes, keeping them at home in familiar territory is best, but not everyone has trusted neighbours or nearby family/friends that can help out. That may be why there seems to have been a huge rise in numbers of cat-sitting services in the last year or two, but most are actually 'cat popping in and out' services?!