The last 'Backing Britain' campaign was way back in 1968; Bruce Forsyth even released a single, which sold nearly, er, 8,000 copies. There were Minis. And peach-faced English girls in wide belts and short skirts. People sent cheques to the Treasury to help pay off the National Debt, and the Postmaster General introduced a union flag letter frank with 'I'm Backing Britain' on the nation's mail. The Trades Union Congress condemned the whole thing.
The firm that started the whole thing off, in 1967, was Colt Ventilation and Heating Ltd. I'm pleased to say they're still around today, and helpfully providing on their website standard specification clauses for designers. I had one such yesterday; my pen hovered briefly before moving on, without leaving the magic words 'Or equal approved'.