It's a small flat in the Barbican complex. Probably one of the ugliest buildings in London. The flat itself is not representative of the photos. It's much smaller and older. The photos are misleading.
The flat was very cold, and the owner had the heating turned completely off when we arrived. The windows are very old and thin, it was impossible to warm up the flat.
Check in was at 16:00 (!!) and there was no option to even leave our luggage a minute earlier.
Overall, horrible experience, I wouldn't recommend it.