In the USA they tried $1 coins. But, seemingly, the public overwhelmingly rejected them - so much so that the US Mint ceased production in 2011. That's why when you go to the US you end up with pockets full of grubby $1 bills.
I can't see £5 coins taking off here until the real value (i.e. purchasing power) is massively less than now. And that could be an awful long way off given where inflation is. Plus, you never know - we might be in the Euro by then ;-)
Another observation on the US. As far as I know, old style $ bills never go out of circulation (unlike here where even the old paper notes were revamped periodically and the old style ones withdrawn).
Thanks for the explanation, I know I have seen and even used them, I would think that they have all been stashed away by collectors whilst probably of little future value. I still have a mint roll of Churchill Crowns bought at face value about 45yrs ago, now worth abut £1.50 each. Hardly the best investment I have ever made but then comes the no point in selling them attitude.
That aside can anyone tell me what is wrong with a £5 coin for general use, does not have to be big and will outlast a bit of plastic a thousand or more times. I would also think harder to forge.