As others have stated, your rights are with the retailer and not with the manufacturer.
However, some clarification is needed. The retailer is only responsible for remedying problems which come about due to an 'inherent fault'. (i.e. something which was wrong with the product at the time of purchase, such as the use of poor quality components or poor workmanship). For the first 6 months after purchase there's an automatic assumption (unless there's clear evidence to the contrary) that any problem which occurs must be due to an inherent fault. Thereafter (for up to 6 years after purchase) it's up to the purchaser to show that the problem has come about due to an inherent fault. Theoretically that might mean obtaining, and paying for, an independent report upon the product. In practice, simply asking the retailer to suggest any alternative cause for the problem might suffice (but it's not guaranteed to!).
Dmbhunt mentions the likelihood of the camera being under guarantee. A guarantee (which is normally from a manufacturer, and not a retailer) is completely separate to your statutory rights. It's a 'gift' and, as such, the 'giver' can determine the terms of that guarantee. If you can't convince Tesco that the problem is most likely to have come about due to an inherent fault, it might still be worth calling upon Nikon's guarantee.
Chris