2. Sign-up to a local coworking space in Central London and make a habit to go there every day. Try to make friends with people there and go out with them every now and then. Many coworking spaces even try to facilitate community building by organising events, etc.
This is an avenue i've been considering. In my case it does require enough budget to allow for a somewhat permanent co-working space setup (big monitor, mouse, keyboard etc), but it's an option.
good luck! treat this budget as an investment into your well-being and social life.
Also, keep in mind not all coworkings are made equal. It might take trying a few before you find one that suits you well.
In my experience small, local coworkings are best for building relationships. Big, chain coworkings like WeWork are the worst. Everyone just minds their own business there.
2. Sign-up to a local coworking space in Central London and make a habit to go there every day. Try to make friends with people there and go out with them every now and then. Many coworking spaces even try to facilitate community building by organising events, etc.
3. Profit.
Socializing doesn't need to happen at work.