Sorry, ExpatPumpkin, your numbers aren't working for me. For 300pw (NB 1 month is longer than 4 weeks...), you're going to get a Very Small and Very Far From The Tube one bedroom flat in Earl's Court. Possibly suitable for one person. If you are working from home for any length of time, it will drive you mad. You may also have issues finding somewhere to sit, and opening your notebook. It will be a nice reminder of the last time you shared a student bedsit with someone

Assuming you want to be comfortable in your home, you will need to do what other couples in London living on 50k do, and live outside of the centre. Zone 2 at least, but probably zone 3. And then travel into town for action like everybody else - getting the last tube home (or even better, the last nightbus!) is one of those unique London experiences

Edited to add - just saw your last post. London is nothing like Madrid - it's bigger and more expensive - and cute postcard villages of the Richmond, Notting Hill or Hampstead kind command a significant premium. Hammersmith is more affordable (but the bus to Boston Manor will take a while...), but not much more salubrious than Earls Court. Have you considered Ealing? Re: websites - Gumtree is your friend