Oh, that's so sad. (I've got 4 cats myself but I still miss their mum, who disappeared a couple of years ago).
A few practical points though:
1. If you need a contact point, so that other AB members might reach you, all you need to do is to create a new email address here:
https://www.gmx.co.uk/
You can then post that email address here (preferably mentioning that it's only a 'throwaway' one) and use it just for as long as you need to. Then you won't risk getting lots of spam getting sent to your regular address.
2. While there are, no doubt, loads of cat rescue centres within the M25, they often seem to make things difficult for potential adopters (and can sometimes demand quite large donations before they'll hand over an animal). Another way of finding some new feline company would be to look on the noticeboards of pet stores for 'good home wanted' notices. Pets at Home have such noticeboards in their stores (Friern Barnet, Muswell Hill, Hendon, Camden, Battersea, Old Kent Road, Wimbledon, Sydenham & Blackheath), as do Jollyes (Dartford, Enfield & Romford) and many local pet shops.
3. If you'd still prefer to go down the more formal route (with potential home checks, etc but with a wider choice of animals available), entering your postcode here would be a good place to start:
https://www.cats.org.uk/adopt-a-cat