Your statutory rights are not affected by the absence of a receipt. (I've had a faulty laminator replaced by Sainsbury's and a faulty power supply replaced by Maplin, both without receipts).
Your purchase has developed a fault within the first 6 months of purchase so, unless there's clear evidence to the contrary (such as the dents where you dropped your camera from the top of the Eiffel Tower), the law automatically assumes that the problem has arisen because of a fault which was present at the time of purchase (such as the use of poor quality components, or poor workmanship). So Tesco is legally obliged to repair or replace your camera. (I repeat that the absence of a receipt does not remove that obligation from Tesco).
Go and hassle them!
Chris