In reply to Dominicandave:
I feel I'm reasonably qualified to offer an opinion here. I have owned a Mini Cooper D for just about a year and have totally fallen in love with it.
My cooper D has been used daily for about a year, having coped fine with multi day Scottish Winter Climbing trips (two people was comfortable enough, definitely not comfy with three). It has been faultless so far (as it should be for a 59 plate with 75000mls). It surprises people speed-wise regularly, especially on twisty roads, so if you like an occasional 'spirited drive', it can be a real laugh. Saying that, it will do 55 miles per gallon while I'm flogging it and as much as 85 when you're steady away on the motorway.. Also, my road tax/VED is £20 a year.
Space-wise it isn't the best, but compared to an MX5 (which I've also had) it is a limosine. If you fancy a bit more load carrying capasity, the 'Clubman' is slightly more practical and equally fun.
One thing to watch is the R56 Cooper 'S'. The N14 engine from 2007 to about 2011 (1.6 turbo) is notoriously unrealiable (have a search for 'Mini owners group' on facebook if you have it). They tend to have countless issues, particularly with Timing chain tensioners (which can be a disaster if they let go altogether). The N18 engine (starting about 2012ish) is notably better (but naturally more costly). If you are insistent on the fun factor, the 06 cars (R53) with the Superchargers are considered more realiable (but obviously age is starting to come into effect to an extent).
A test drive will probably have you convinced either way. Well worth testing the Cooper Diesel in my opinion.
(Worth baring in mind, my family/friends/girlfriend/colleagues/neighbours/etc all think I have terrible taste)