About the 5 main airlines firms based in the UK.

It's part of my Economic classwork....Thanks for your help first....
Which five would you consider to be the 5 main airline firms based in the UK?
I personally think of
1. British Airways
2. BMI (I forget its name in full)
3. Virgin Alantic

I am also thinking about easyJet, and some other low-cost airlines.
But the problem is I can hardly find out where these airlines are based.

Please may someone help me to sort out my questions. Thanks.

BMI=British Midland International...
I think 5 biggest UK based airlines would be:
1) BA (Biggest carrier in UK)
2) BMI (Second biggest carrier in UK)
3) VS (Second biggest long-haul carrier in UK)
4) Easyjet (Biggest LCC in UK)
5) FlyBE (Biggest regional carrier in UK)...

Other airlines that could go on the list:
FlyGlobespan (First Scottish LCC)
Monarch Airlines (Possibily the largest charter airlines in UK that is not in a group)