Just checked, it was Double Two, first made in Wakefield. So called because the shirts came with two collars, and two sets of cuffs, so they could be replaced when worn without replacing the whole shirt. They were made of terylene, which never needed ironing.
The polyester fibre it was made from under the name terylene was invented during the war by a scientist from ICI and he approached double two to use it for a shirt. www.doubletwo.com click on company history.