As genuine as a 40 pence piece 

A term used in the UK when someone is desperately trying to convince you that their piece of information or version of events is correct to gain your trust but you know that they're blatantly lying through their teeth. Or someone is trying to sell you the latest designer object (watch, trainers, handbag etc.) and you can clearly see it's a fake. It's as genuine as a 40 pence piece. There is no such thing as a 40 pence piece in UK currency so if someone tried to give you one you'd know it wasn't real money.

A woman looking at handbags on Ebay: "oooo have you seen this lovely designer handbag it's only £10"
Friend: " narr mate it's a fake"
Woman: " it looks genuine to me"
Friend: " genuine! It's about as genuine as a 40 pence piece"

Or

A man after been told someone unreliable information: " rubbish! what a load of old tosh"

The informer: " narr mate it's absolutely genuine"
Man: "yeah about as genuine as a 40 pencepiece"

As genuine as a 40 pence piece by hteb78 January 23, 2024