I thought fake £1 coins were more common than that. Probably about one in every twenty pennies I receive has a cent in it, or with 5p coins - a dime. I realise these aren't fake, just foreign, it's just my random observation.
Fake £1 coins I remember my sister discovered when we were kids, at the time they sounded different when dropped.
These days the last I heard, the engravings on fakes aren't as decent as genuine coins, sometimes the Queen isn't quite detailed enough and she's isn't quite in line with the design on the other side.
I sometimes keep £2 coins that have designs I haven't seen before. I think they're cool.
The new fivers are pretty, I think all paper money is pretty really. You don't need to hold the new fivers up to the light to see the "watermark". Some parts of paper money are raised, such as the bit that says, "Bank of England" in stylised writing (it's flat on the other side) and the bit below it, "I PROMISE TO PAY THE BEARER...". I've noticed the new fivers have that feature still. They're hard to fold, they're plastic and bounce back up and don't stay put. They also spring out of your pocket if you're not careful.
Also, most people probably won't notice this, but under the clock tower, where it has a hologram saying Five/Pounds depending on where you flip it, underneath in small text it says "£5". There's a £ sign to the right of the clock tower. Yeh, I notice stuff like this which bores other people to death. Oh well.