There were plastic £5 notes available for a while here in NI, but they've all been withdrawn from circulation. If there was some kind of a fault with them has it been fixed now that the Bank of England plans to introduce them?
We've had "plastic" notes for a few years now. You have to be very careful when you're using them as they are so thin and tend to adhere to each other: it's easy to hand over two twenties instead of one especially when they're fresh out of the bank machine.
New Zealand and Australia have been using them for years. They are not bulky. The first ones they used in NZ the dye wore off but they have perfected that now.