Do they do maintenance over the Bank Holiday?

My speeds have been useless over the weekend - so low that none of the speedtesters would load and it took over a minute for a simple page to display. Suddenly this morning I have 18.8Mbs via ethernet and 15Mbs over wireless. I didn't do anything except reboot the modem and router a few times. 'Essential maintenance'? I'm in SE London. Shouldn't they warn us if this is going to happen?

I suppose they could warn about scheduled maintenance but if it's essential maintenance it sounds like it's too late. Did anyone else suffer?