No they didn't. Typical Daily Mail invention 0% based on fact. The EU did not have officials over here checking on food labels etc.
And we were only ever half-assed metric anyway: pints etc in pubs. Miles not kilometres. Lots of food sold in 454g (1lb) packs. Same with our membership of the EU : not in the Eurozone. Not in Shengen. A big budget rebate making our contribution the lowest % of GDP of any member. And in return, we had lots of lorry drivers and no empty supermarket shelves.
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The only generation comfortable with Imperial-only is the faux-nostalgic old fogeys who won't be around very much longer.