This is a tough question, for which the answer will either be as clear as day to you, or you will 'umm and arr' about for years if given the opportunity.
Essentially speaking, I was in your position a few years back, and stubbornly elected to straight in to a well known integrated cadet course offered by an established flying school almost immediately after completing my A-Levels at a traditional Sixth Form, instead of attending University.
With hindsight, I now wish I had attended University for a plethora of reasons which I'll list as follows:
Maturity:
You may feel and look mature, but the simple matter of the fact is, between the ages of 18 and 21, there is still a vast amount of maturing for you to do regardless of how you feel upon leaving A-Levels or College Education. Furthermore, your flying course mates will either be in the same boat or they won't and you'll have to accommodate that.
Education:
It's in the title, not only do you get an education to a discernible level which can be applied to Plan B, Plan C or Plan D, but you get an education in 'Life' that you won't have necessarily obtained living at home with the parents, doing A-Levels or College studies.
Your CV:
From my very recent experience in job hunting as a 200hr Cadet Pilot, it would appear that for this position an individual with 'any' degree (i.e. something substantial, and not in beauty or hair products) would be more appealing than someone without a degree. Plus, it's a great filler even you have a relatively vanilla piece of A4 with not much on it.
Plan B, Plan C and Plan D:
Take a degree that can help your Plan B, Plan C and Plan D - something irrelevant to aviation in some respects, but on the other side of the coin, can be beneficial to you in your potential future aviation career. Prepare for the future, you cannot plan, but take things in to account - there could be another recession, or there could be vast numbers of cadet pilot recruitment in the next 5 years. Have alternate Plans B, Plan C and Plan D at the ready - just in case.
What did I do?
I finished my training in late 2011, commenced a Part-time Degree (Education) in early 2012, established a Company unrelated to aviation (Plan B) in late 2012 commenced employment in Flight Operations (Plan C) in early 2013, and then found a job with an airline recently.
If necessary, look in to government grants. But always focus on the 'Bigger Picture' - education is an investment and at the very least that extra line on your CV could one day land you that dream airline job.
Lastly, ignore the flack that you'll receive from some cynical and pessimistic individuals and never, ever give up. Ever. I mean it. 
Don't hesitate to drop me a PM if you've got any questions, I know how tricky this is for those in your position. Good luck with it all.