We've got a beastie now in the UK called the NPPL which is a low(er) cost recreational license. I'd suggest you go for one of those, if you feel the need to upgrade later because you don't like the limitations (size, weight, day-VMC) you can, but in the meantime it'll get you airborne without soaking up too much of your service pension.
NPPL (National Private Pilots License) can be obtained with one of three ratings which are SEP (Single Engine Piston - light aircraft to you), Microlight or SLMG (Self Launching Motor Glider), and you can add the other ratings on at your discretion.
As a rough rule of thumb, getting the Microlight NPPL will cost you about £2k, whilst either of the others will cost about £3k, adding any other rating will cost you about £½-1k. [So, it's almost certainly cheaper to go microlight then SEP than the other way around].
SEP
Basically this qualifies you to fly the conventional club light aircraft, Pipers, Cessnas, Jodels, etc. as well as a wealth of interesting PFA homebuilt aeroplanes that you can either build yourself, or buy secondhand.
Your typical light SEP probably cruises around 70-110 knots, with an endurance of 3-5 hours.
Costs? Hire around £80-£150/hr, a cheap second hand Cessna will cost you upwards of £15k and cost £50-£100/hr to run. Alternatively PFA types start around £6k to buy, and cost probably £35-£70/hr to run. You can join a syndicate, purchase costs of a share could be anywhere from £1000 upwards, and running costs probably about half the hire cost of a similar type.
Store in a hangar or a tie-down.
Microlight
Qualifies you to fly microlights, which are little single and 2-seat sports aircraft defined by weight and stall speed. In performance, there's a clear overlap between the faster microlights and the slower SEP. Like SEP, oodles of types and oodles of clubs out there.
The typical microlight will cruise at 40-90 knots, with 2-3 hours endurance on an older type, and the newer types would give yer Nimrod a run for it's money, and certainly out-do your bladder.
Costs? Hire only became legal a fortnight ago and doesn't allow pax carrying yet, but hiring will certainly be an option by the time you're qualified. I'd guess that microlight hire cots will be around £40-£80/hr. Alternatively, a good second hand 2-seater will set you back anywhere between £3k and £30k depending what you want, and running costs are likely to be in the range £20-£40/hr. Syndicates exist to, and pretty much the same principle applies as SEP.
Store in a hangar, or de-rigged in a trailer or garage. Some types will take being tied- down for long periods, but most won't.
SLMG
An SLMG is a fast touring or soaring aeroplane that eats a lot of runway. They suit either glider pilots who don't want to have to get a launch, or people who like cheap long distance touring.
Costs? Probably £15-£50k for an aeroplane, hire opportunities are rare (as, I should mention, are schools, this is a minority occupation compared to the other two). Running costs, are probably about halfway between microlight and SEP. Will need hangaring, which can be expensive in some parts of the country.
I'd suggest in your quest for knowledge you look at joining PFA and BMAA, or at-least phoning them up (01273-461616 or 01869-338888 respectively) and asking for some information. Also buy a few issues of Flyer and Todays Pilot from WH Smiths which are both great on explaining the sort of stuff you're interested in (and full of adverts from flying schools and people trying to sell you aeroplanes as well).
Best of luck,
G