Soooooooo many comments following thoughts during the day so this is going to be a mammoth post.
But first, a bit about 5th Gear. Basically, when the original Top Gear got cancelled, virtually the entire cast decamped to Channel 5 (hence 5th Gear) and started the programme again in almost exactly the same format. The current Top Gear was launched afterwards and is essentially a new programme with an old name. That's why you'll hear reference to "New" Top Gear and "Old" Top Gear.
Mini Cooper S (new, not old): I'm not decrying the abilities of the car, but to be cool ability is not enough. The trouble for me is that around here there are so many that about 99% of people driving are trend followers rather than trendsetters, ergo the car must be at least uncool, maybe even seriously uncool. I can see the Fiat 500 achieving similar status in a few years as there are already quite a few about, but for now it seems there are few enough that it is mainly the trendsetters who have them.
Fiat Panda: Yes, it does only have 60bhp, but to focus on power is to miss the point. Basically, you are looking at a tiny little car (thing Chevy Aveo size) which you can drive almost anywhere. At school, one of my friends had the original 1980's version and I can confirm that that really did go everywhere - we once drove it across the proverbial ploughed field to try and get it stuck, and failed

But, that car rusted away in under 10 years - the moment when another friend pulled the seat up without using the proper lever and ripped up a large part of the floor put the final nail in the coffin. OK, it's slow on road, but it has to be cool (or sub-zero) just for the fun and go-anywhere factors.
Smart: Seriously uncool. Yes, it's small and can be parked where other cars can't, but would you really want to drive one?
Other suggestions: Citroen Berlingo - Cool.
http://www.citroen.co.uk/new-cars/citroen-berlingo-multispace/media-gallery/360-exterior/Yes, I'm disagreeing with Kev on this one. i know it's a converted van and is making absolutely no attempt to be cool. But, that is what makes it cool to me - by driving around in one of these you're sending out a message that you're someone who doesn't need a super-stylish car to look good. Instead, you've gone for a cheap, spacious, tough car which is a decendent in spirit of the Citroen 2CV - it's the sort of car you could imagine a French peasant chucking 3 sheep in the back to take to market. The Renault Kangoo is similar, but not cool on quite such a level to me.
Land Rover Defender - Even more so than the Jeep Wrangler, it's barely changed in 60 years of production. No compromises, it will take you almost wherever you want to go whatever the terrain. Those looks may not have changed, but like the Porsche 911 have matured with age. While other 4x4s may cosset you at the expense of off-road ability, the Defender is built for the British farmer to carry 10 sheep in the back

. You rarely see one which isn't used off road, so you know it's been bought for a purpose, not to create an image. To me, this one is sub-zero.
Honda Fit - This looks a lot like our Honda Jazz which is the process of being replaced. Believe it or not, i think your adverts are better than ours!