I have lots of £80/100 large 3 story double fronted fronts in central london, having houses worth over 10 million i think £80 for a clean is acceptable. In NW8 i have 2 monthly customers next to eachother who i charge £250 each for in and out which takes a day, They are filthy rich and dont bat an eyelid paying me, 1 has the key for the other and pays for both. Have canvassed the road and roads around it but cant pick up anything else which is a bugger as would be the ultimate.
Depending what part of london but £30 could be reasonable.