UKC

Where can it be purchased? 

Probably the Alpkit Project, which is significantly cheaper than the obvious competition (e.g. Moon Saturn). I've not used one so can't comment on them properly, but I'd assume that the closure and carrying systems are less fancy than on more expensive models; on the other hand, Alpkit are really good in terms of warranty stuff, and when the outer shell of my small pad (which was three years old) was trashed they replaced it for free.

Psychi do a tri-fold about the same size but slightly thinner for £40 less.

I was dead impressed with the Psychi tri fold when I fell onto one a few times. Great pad for the price. 

Absolutely hateful to either carry or put into a car mind

I’ve got the bi-fold and for the price it’s been fantastic. I think the foam is starting to weaken ever so slightly but only after two years of very heavy usage.. the outer is (aside the mud embedded in the baby blue) still in decent condition.

For size/cost ratio it is hard to beat the Samual Smiths one I got for free from the Blue Bell in 1986.

Yeah. I think they go on offer a lot. Two of these and a sit pad and you're sorted. 

Moon Saturn at £233 at a few places now. Bigger, deeper and better pedigree I would say than other mats mentioned 

I've ordered the biggest alpkit pad which seems the best value of the 3 mentioned to me.

You should have checked out Ocun Bouldering Mats.

I second Droyd's Alpkit recommendation. Used a project (hired for the occasion from Alpkit) in the Lakes last time we were there without a pad and it's pretty decent. Heavy bugger mind, and the straps aren't as comfortable as Moon's but still managed a 3 mile walk-in with it without any trouble.

These do look good but the large pad is not the widest (100cm) and only 10cm thick. The Alpkit does seem like the only viable (cheapest) option compared to the Moon, but seems a bit of a gamble atm (see previous reviews on here).  I’ve had a few Moon pads in the past and the foam hasn’t been great but the rest of the design was excellent (carrying/reverse pad thing/materials) I’m  just hoping that the foam is better this time around. I’ve just ordered the Saturn from Absolute-snow with a 10% discount for £215 so will report back!

Good choice. I've had a dozen trips to Font in the last two years alone and have landed on just about every type of mat. There's a good reason I own the Saturn. I had a spinal op years back. Nothing beats the Saturn, especially from above 5-6m. The Snap large is a good equal. I'd suggest going cheap is a false economy...

I have the massive alpkit one but it's a proper pain in the arse to carry. I've had big pads before (moon Saturn) but this moves about too much on my back. And you better hope it ain't windy. 

Do you find the double mat is big enough for using on its own? I'm considering one myself and not sure whether to got for the double or triple. 

Generally yes, though I tend to shy away from anything highball that's above my onsight grade and traverses that are above a few feet. Lower traverses I'll just stick it under what I think is the crux...