Airtours became MyTravel.
Flying Colours became JMC became Thomas Cook.
These two merged (with a few others I've missed) to become (still) Thomas Cook. Their callsign is Kestrel.
Britannia became Thomsonfly.
Air2000 became First Choice Airways.
These two merged to become Thomson Airways. Their callsign is Thomson.
It's been that way since about 2008 so just as that becomes clear stand by for the next re-shuffle! (No, I don't know anything, just guessing)