This has been discussed many times on here, so it may be worth having a search for similar threads and giving them a read.
It's always difficult to judge whether a degree is going to be worth it or not, and the arguments for integrated training versus modular training always appear here. If you are applying for a sponsored training position such as that offered by CTC, Cabair/Flybe etc, it is arguable that a degree would be beneficial in that it would make you more attractive than someone with similar background but without a degree, especially if said degree is related to aviation.
However, if you go the modular route and work a job alongside your training as you pay-as-you-fly, as it were, then, in my opinion, your flying experience/currency/ratings will probably count for more than a degree when applying for a first job. On the other hand, if you end up in the pool of unemployed commercial pilots chasing jobs then you'll need something to give you the edge, and a degree might be that thing... so you see it's swings and roundabouts.
Financially, as you have been working for 3 years you would be classed as an independent student and therefore you qualify for financial assistance not offered to those coming straight from school, such as a £1000 grant each year of your degree, which, by definition, you don't have to pay back. You can also get grants by way of the hardship fund, so if you're skint and can prove it, you get more financial help. You'll still be in a lot of debt in terms of student loan, but it's the cheapest loan you'll ever get and you don't start paying it back until your salary reaches a certain threshold. If you earn that salary as a commercial pilot, for an airline say, it will be a small fraction of your monthly pay that you'll never see.
One plus point is your age, you're still young, and if you're quick you MAY get a uni place this year so you'll be about 21 when you're done.
Otherwise, work your socks off and perhaps take out a career development loan to help fund training, get several hundred hours with a CPL/IR and AN INSTRUCTOR RATING as the best way to stay current and employable as a pilot, and fire off CVs left, right and centre to land that first job, if the airlines is where you want to go.
It may be worth noting that several sources indicate that the rate of expansion and pilot employment/training has never been so high and is set to remain high, or increase, in the years ahead. So, consider that when you decide what you want to do. As for actually predicting what the industry will do in 3 years time, it's hardly an exact science. I was in your position some years ago now but the decision was largely made for me thanks to Sept 11th. The chances of sponsorship, or even a commercial job of any kind, looked immediately bleak, so I went to uni to wait until it picked up.
Remember also that it's not all about the job: uni will be a great experience, you'll meet new people and you'll have a fantastic time.