This is taken from a local gov website. I'm sure there is something similar on the Trading standards page.
know your consumer rights - Warwickshire Web
Normally, it is your responsibility, to prove that the goods were faulty at time of sale. However, in the first six months from the date of purchase, when you return goods to request a repair or replacement, (or following that, a refund) you do not have to prove that the goods were faulty at the time of sale. There is an assumption that the goods were faulty unless it cane be proved otherwise by the trader. If you choose to ask for a refund rather than a repair or replacement, the onus remains on you to prove that the goods were faulty at the time of sale.