Don't know if this is store specific - I found these in the Tesco Extra in Cumbernauld.
Pack of 5 making them just over 4p each. There were loads left about an hour ago.They were £1.20 so 80 per cent off!!!
Double seal Peel and Seal closure
Displays TAMPER EVIDENT message
Sequentially numbered for track and trace
Burst, Tear and Puncture resistant
Easy to write on surface.
Royal Mail pricing in proportion with approved Large Letter size.