Most supermarkets sell chestnuts for roasting or making stuffings at this time of year Simon.
I have been getting a bag or two each week for the last 4 or 5 weeks. They have dropped to about their cheapest for this year last week in Morrisons, they started off a few weeks back at £2 per bag of 300gms but Asda had them at 2 bags for £3. Morrisons has dropped them now to 2 bags for £2.
If you decide to give them a try you need to cut through the outer shell, more like a hard skin than a normal nut shell, on one side, make quite a large cross. Then place on a baking tray in the oven at around 200/220c for up to 15 minutes. A little water in the tray helps to steam them open a little more than if totally dry. If you dont cut them they explode in the oven as I found out when I did them the first time about 10 years back
Theyre very hot when they come out of the oven but I try and peel them as soon as I can handle them as the edible bit inside never seems too hot to eat and theyre so much nicer when hot than cold