If you're looking for no frills stay in London - London Lets are great.
There was a 11th hour change to my accommodation from the one I saw online. I wasn't pleased with what was offered - which was actually closer to the city - but I was was sorted out with another place near where I wanted to be - Wapping. This was done quickly and without fuss within the hour on a Sunday evening prior to my stay!
Good communication by Kamal and his associates throughout - which is always reassuring.