Been keeping my eye open for a winter bag and found this.

http://www.millets.co.uk/camping/sleepi ... ute=628528

This looks like a good price for a down 4 season bag. Saw one today in Millets and the pack size is quite small and it weights in at 1.2 kg. The reviews seem odd though since they are so conflicting.

Can't help thinking I'd be better off saving a few more pennies and going for a well known brand though (eg a pipedream)

It looks a great bag for the money, but be aware it isn't going to be anywhere near as warm as it claims. The -21C rating is misleading as I suspect they are quoting the extreme rating at best.

The 500 will refer to something.

If it's 500 fillpower down, at 1.2kg it won't be comfortable at much less than zero.
If it's 500g of down, then even if its top shelf 800eu down (it's more likely to be <500) and constructed in a good design then -10C could be achievable.

That said, for £60 you could boost it's rating with a decent insulated mat and a cheap down jacket and you'll have a very versatile 4 season set-up for the average UK winter for under £200.