This offer started today in store and is also on-line. As mentioned in the Daily Mirror
Tescos is focusing on a new price war by cutting the price of prescription glasses to £10. That is the all-in cost from today for a frame, from a choice of 12, plus lenses and a free eye test. Similar spectacles in rival supermarket Asda cost £50. At Specsavers and Boots they are £25.
I ordered a pair today as a spare set for the office
hope that helps someone