Hi Jamie,
Have a look at the section on
www.balpa.org for aspiring commerical pilots. This will give you an intro to the routes to becoming a professional pilot. Then go to the Wannabes section of this site, set aside a fortnight
and have a read. There's some very useful "sticky" threads at the top of the "Professional Pilot Training" and "Interviews, Jobs and Sponsorship" forums - have a good read through those as well.
In summary - you can get into commercial flying by going down two main routes - be very lucky and get some kind of sponsorship from an airline or pay for your own training.
Sponsorship places are few and far between and are very, very competitive. The CTC Wings sponsorship scheme is one example (
http://www.ctcaviation.com/wings/). Some airlines have their own schemes but the overwhelming majority don't sponsor, at least not at the moment...including BA before you ask! British Airways stopped sponsoring wannabes a few years ago.
If you go down the self-funded route, expect to have to pay anything upwards of around £30,000, if not more...depending on what type of course you do. The cost will vary but will still be in the tens of thousands.
Also have a look at the LASORS document on the CAA's website - it has all the nitty gritty details of licence requirements etc.
There's an OVERWHELMING amount of info out there - a lot is on this site or at least pertained to on it.
I've just finished university and am currently doing the PPL before trying my luck at sponsorship.
Hopefully this is enough to get you started. It'll take a lot of research on your part but you'll learn a lot about how the aviation world works as you browse.
Best of luck
V1R
P.S. Also be sure to check that you can get a class I medical from the CAA - no medical, no flying
P.P.S. Talk to your instructor/s - see what advice they can give.
P.P.P.S. There's a strong chance that any question you can think of regarding flight training has been discussed somewhere on this site - make full use of that search fucntion on the top left of the homepage!