Hi Martin, welcome to pprune. I must admit I was in exactly the same position as you, almost finishing uni in Glasgow and wanting to pursue a career as a pilot. Read this and other websites as much as you can, it contains a wealth of information and will likely as not answer most questions you've got. Look at the sticky thread at the top of the professional training and groundschool forum to get you started!
To answer some of your questions specifically, I wouldn't get too concerned over the maths requirement. I've done all the theoretical exams and there's not much above standard grade mathematics in there. As for when you're actually flying, as long as you can do some simple mental arithmetic, you should be fine.
I would advise doing the gapan test, as it should give you a good idea whether or not you have the aptitude for flying. Also, definitely go for a trial lesson or two to make sure you enjoy flying! I'd recommend going down to Prestwick as the flying club there is a good bit cheaper than the one at Glasgow.
Assuming you like it, and want to pursue it, the next most important thing is to get yourself down to Gatwick for a class 1 medical, as without this there's no chance of a career as a commercial pilot. I think this costs a little over £400 nowadays.
British Airways don't sponsor people just now (since 9/11) but CTC McAlpine do, so it would be well worth getting in touch with them. Also, Britannia tend to run a sponsorship scheme for people in your position (ie. little or no flight experience). Also worth contacting is Atlantic airlines at Coventry, who run a cadet scheme, but I think you need a PPL before you can apply. There's one or two other airlines that sponsor from time to time but they tend to be part sponsorships, meaning you're paying up to £30k of the training costs.
Hope this helps.
PW