BBC ONE and BBC TWO downtime

Just noticed on the Sky EPG that BBC ONE and BBC TWO both have downtime on Wednesday and Thursday morning, around 4am. EPG entry has "This is BBC ONE" and "This is BBC TWO".

Is this something relating to the power cuts last Friday, or I wonder if it is the annual re-broadcast tests?

Although you can be forgiven for missing it due to the somewhat misleading thread title, this is being discussed here.

Ah, thanks Nick. I thought it was unusual it hadn't already been mentioned.