After purchasing petrol this morning and using the 5p a litre voucher, the assistant asked me if I had any more as Tesco are now accepting 3 at a time. I assume they have changed their policy now morrisons are offering the 12p deal.
If you don't have any vouchers visit ebay. There are loads for sale (just search tesco petrol), this particular deal is for 12 at £4.40. I normally save about £3 on each voucher, so this can easily earn £36 (depending on how much you fill up)