Called into my local Tesco at Meir Park, Stoke-on-Trent, today and discovered that all Virgin Mobile and T Mobile airtime vouchers were reduced by 20%. I bought a £10 Virgin voucher which shows on the receipt as £9.78. With the 20% discount of £1.96, I paid £7.82.
The lady at the customer services desk said not many people knew about the deal as it hadn't been publicised very well.
Although the tannoy annoucement specifically mentioned the 2 networks, the receipt states '20% off all top up cards'.