Fuck, I paid $1850 for a 650 sqft one-bedroom in Mountain View. That was before they tried to raise the rent after the Google expansion, I hear they posted it at $2400 after I left.
My 3 bedroom 1000sqft house with a garden in London has a current rental value of about $1600. That's the difference between living in a leafy, relatively unfashionable suburb in the South of London vs. living in one of the enclaves of rich people or hipsters in the centre of town. I have a 45 minute commute to the centre, door to door.
The analogue is living in Oakland or San Jose. Of course public transportation is much worse in the bay area, if you happen to live and work near the right Caltrain or Bart stops then it can be comparable.
The place I lived in Mountain View was prime real estate. I was on Castro street, one of the only walkable places outside of San Francisco proper. There is plenty of cheaper real estate in MV.
Similarly in Battersea I live near Clapham Junction. I can get to Heathrow in 40, Gatwick in 30, Soho in 25 and Bright on 50! I can also cycle to Trafalgar Sq in 20 mins if the lights are favorable. Again, there are cheaper places around, but not without worse location or other problems with the property.
Also, the first property on the link you listed is £390 a week. You do realize that that is $2700 / month right? And you do realize that in Mountain View when you rent there is no council tax, and you don't pay estate agents any fees at all. In fact there are no estate agents, and property holders often give you some kind of deal like reduced rent for the first month to get you to sign a lease.
That said, London is more expensive.