I spent £14 in Robert Dyas (Oxford) yesterday.
With my till receipt they gave me a voucher for £5 off a £10 spend, valid for one day only (this Saturday, participating stores only, see instore for T&Cs).
Sorry for the few details, but hopefully this will be useful for someone needing to make two small purchases this week.
Robert Dyas are good for batteries and kitchenware and often have cheap telephones, shredders etc. in store.