Hi - have you googled to see if there are any guinea rescues near you at all, or within driving distance, there is a fab one near us in Hampshire. You could start a thread on here to see if there are any takers, putting West London in your title thread.
It is hard to think about rehoming pets, but a home where guineas are being hassled by cats is far from ideal for them, so hopefully someone may be able to offer a cat free situation for them.
The Piggy Bank UK is a national support network that enables rescues to work together to rescue and rehome as many guinea pigs as possible.
Some readers here will remember that afew months ago a lady on another website needed to rehome a large number of guinea pigs. Well some of her boars went to a piggy bank rescue. Which means if they were not able to find them homes in that area, they could have asked for help in another.
And yes it has been known for SFA readers to rescue piggies