A couple years ago in London, I seriously confused a young retail clerk by presenting her with Scottish banknotes presumably left over from an earlier trip to Edinburgh. She had to go get her supervisor to assure her that this was indeed real money.
OK, it's more "real" than an IOU I hand you, because I know that in order to issue their IOU they actually had to deposit an equivalent amount of cash with the Bank of England, but it's not legal tender -- while in practice pretty much anyone should be comfortable using it as a medium of exchange, the only _guaranteed_ use of a Scottish note is to exchange it with the issuer for a Bank of England note (or, in Scotland, coins), which you can then proceed to use to pay your taxes or other bills because they _are_ legal tender (value limits apply to specific denominations south of the border, you need to use pound coins north of the border).
But yes, in practice, real money. Just don't try telling anyone they've _got_ to accept it, because there's no such obligation.
From the Royal Mint's website:
> Legal tender has a very narrow and technical meaning in the settlement of debts. [...] It does not mean that any ordinary transaction has to take place in legal tender or only within the amount denominated by the legislation. Both parties are free to agree to accept any form of payment whether legal tender or otherwise according to their wishes.
Most of the time most of the people are happy to accept anything that's a properly denominated bank note. But while I'll happily try to spend Scottish notes down South, there's no requirement on any shops to accept them.
Edinburgh Council have recently done something interesting though: they've stopped (in most locations) accepting cash for payment of bills. Now I'm wondering if I should cancel my direct debit and take them a stack of pound coins :).