In reply to neuromancer:
I work for Decathlon, so have a bit of experience of their products.
As others have said, the £39.99 mountaineering trousers are really good for the price. I had a pair a few years ago and slimmed out of them, but I'll replace them this year with the same. As far as clothing goes, the Simond name is being applied to climbing/mountaineering stuff that used to be branded Quechua/Bionnassay. You'll see otherwise identical items with the two brand names on; my Simond Alpinism 32 rucksack has Quechua tabs on the zips. I don't know for sure, but I think Simond are still producing the hardware themselves.
I've found the Simond climbing jeans good. They have a nice cut, are easy to move in and are made from stretch fabric:
http://www.decathlon.co.uk/jean-man-trousers-id_8175777.html I don't think any UK store keeps stock of them, but they can be ordered if you ask.
I'm not so keen on the Mideet midlayer posted by Neuromancer. It might be perfectly good, but the colours are usually vile and it feels a bit cheap (but then, I suppose it is!). Decathlon use duck down; cheaper jackets use 50/50 down and feather, better (Bionnassay) ones use 90/10.
I've spoken to a few guides who swear by the yellow leather Alpine gloves (again available to order). I have a pair, and I'd say they are well made and fairly warm, but I don't have enough experience to say how good they are. I've also got a pair of the Bionnassay 700 gloves which I really like, though again I don't have enough experience of other brands to really compare.
The crap Vuarde Vulca shoes mentioned by TryfAndy have been replaced by the Simond Rock, which looks miles better:
http://www.decathlon.co.uk/rock-id_8230651.html A few mates climb in Vuard Techs and find them good; I will be buying a pair for indoor soon:
http://www.decathlon.co.uk/vuarde-tech-id_8091313.html
If you see something on the website and can't find it in the store, ask and it might be possible to order it in, though there are sometimes infuriatingly long delays if the warehouses are also out of stock.
I hope that's of help to people.
Matt