I wonder if they have tried the Mayhew - they offer emergency foster care
http://www.mayhewanimalhome.org/whatwedo/needourhelp.html - It says they were set up to help the starving, abandoned animals of London
"The staff of The Mayhew Animal Home are non-judgemental and aim to offer advice, care for and rehome animals that you can no longer care for, whatever the reason. Please note that there are a large number of animals needing this type of help, but we will help or advise wherever we can. If you need us to to take in your animal for rehoming please call us on 020 8969 0178"
Also, I assume they have contacted the local CP?
Not local, but Romney House rescue in Bromley Kent (about 15 miles from Kings Cross) - Silvana won't turn a cat away if she can find the room. Not ideal re distance but if these poor cats are going to be put out to fend for themselves, worth a try?