How many fake One Pound coins are in circulation?

Answer 1

It is unlikely that there are any fake five pound coins in circulation simply because they are commemorative coins and therefore do not see much circulation, you'd get enough funny looks as it is trying to spend a 5 pound coin. However, there have been reports of people passing off 25p crown sized coins as 5 pound coins. If the coin doesn't say "Five Pounds" on it (and it isn't a gold 5 pound coin!) it has a face value of only 25p.

Answer 2

From its 2009-2010 Annual Report, The Royal Mint advises that as of 31-Mar-2010, there were 1,474,000,000 One Pound coins in circulation.

The Royal Mint further advises that -

Regular surveys are undertaken by the Royal Mint to establish the incidence of £1 counterfeit coins. The most recent survey indicated a counterfeit rate of around 2.5%.

That is about 36,850,000 fake One Pound coins.

Answer 3

The Royal Mint estimates that approximately 2.5% of circulating One Pound coins are fakes.

See the link below for a Royal Mint article on counterfeit One Pound coins.