Update (1st March 2013): I have done a eShop versus Topcashback comparison, to determine which route returns the greater number of Avios. You can see the results here.
Many people now use Cashback sites to get a few percent back on their house and car insurance, mobile phone, utilities and groceries. However, Topcashback has just added a new option where we can convert our cashback into Tesco Vouchers, with a 5% bonus. From, there, you can then use them as normal, including converting them into Avios.
There is a limit of £50 per year per account, but this is still a very good deal. £50 cashback gives £52.50 worth of Tesco vouchers which can be converted into 12,600 Avios at the standard conversion rates. However, Tesco has fairly regular 30-50% Avios conversion bonuses, so you can get even more.
But, even at the standard rate, you’re paying 0.4 per Avios, which is a very good deal.
If you’re not already a member of Topcashback, you should head over there and register. Even if you are already a member of another cashback site, such as QuidCo, it might still be worthwhile joining Topcashback – it has the added benefit that it does not charge £5 per year.