I am not sure that you can buy them in UK (I don't remember ever looking) but an earthenware chestnut roaster is cheap and perfect. Put the charcoal in the bottom, fill the top part over the coals and away you go. Sprinkle some salt crystals onto the nuts as you put them into the roaster and there you go, perfect roast chetnuts.
Here they are also boiled then peeled and dipped, while still hot, into salted butter.
There is a festival here (S. Martinho) which is celebrated by eating fresh roasted chestnuts washed down with a specific wine the name of which I cannot remember.
ETA 30 mins seems excessive, I usually do them for about 10 minutes.