As stated by lCG the Distance selling regulations 2000 permit you 7 working days from the day after receipt of the goods to cancel your order but not if it has been specifically made for you which I would find difficult to believe as stated by craft, elvis & puternut, if next day delivery was offered.
You should do this in permanent form (email is considered permanent) stating you are exercising your right to cancel the order under The Consumer protection (Distance selling regulations) 2000.