JMC,
Been there not too long ago and know exactly what dilemma you are now facing. My advice, go for it. If aviation is something for which you are passionate about then you are unlikely ever to have such a desire for any other type of employment.
You really must decide what exactly you eventually want to end up doing. If your eventual aim is to become Flight Crew, then uni would now be a good choice as increasingly the airlines require a degree of some sort (generally a maths/science subject is good) for placement on a 'cadet' scheme, as mentioned...such qualifications are also useful (although not neccessary) for careers such as ATC.
Money, isn't however everything and if you are not particular about which area of the industry you favour there may not be a need for uni. I personally wen't straight from 'A' levels to a summer season with a handling agent, and have never looked back. After 6 months at this I'd gained enough experience to be accepted as a junior Ops Assistant, and have since worked my way thru the ops department, where, for now, at least, I earn a damn sight more money than 80% my fellow college mates who went on to uni, and are now working in the local supermarket.
As pointed out, temp. work with handling agents isnt easy, and the money IS poor, however, it is one of the only decent ways of getting into the industry with little or no experience. PSA's work long and unsociable hours but my company (at MAN) always had plenty of overtime up for grabs which could bump up your wage considerably. The job can be stressful and the hours crap, but we always had a good laugh on the Terminal 2 night shift
Let us know what you decide ... best bet for handling agents at BHX - aviance/servisair (wouln't bother with BA, i'd say you're a tad young), or BMI/servisair at EMA. Hope this helps.
TT