As far as I'm aware they stopped accepting cheques at all mainstream supermarkets ages ago, even the smaller Spar shops and the likes of Londis chain of corner shops have cash machines now, therefore they expect you to draw out the cash.
You could try the, Yell directory site below, put your postcode in the box on the top right and look for your nearest cheque cashing centre, they will accept a cheque covered up to the amount of your card, although they will charge you commission.!
http://www.yell.com/super/cheque+cashing/united+kingdom?sem=g&cam=cheque+cashing_legacy+geo&refcd=GO488T2305182S_cheque_shops&tsacr=GO1052953404