For UK, it looks for a special mark being used by ITV companies (and Channel 4, which are ultimately controlled by IBA) which is mainly used to signal companies in other regions that they should switch to an advertisement tailored for their region [1]. Since the television channels were controlled by IBA and BBC, this is a for-sure way to skip advertisements.

1: https://en.wikipedia.org/wiki/Cue_mark#Cue_dots_in_televisio...