The question of legal tender is of course mute nowadays: a cheque, PO, or credit card isn't legal tender either, they are forms of recognised currency. The same is true of Scottish money: it is at the discretion of the seller whether they accept it, although they are legal currency they must be backed up in equivalent tender (basically, private banks print Scottish money, and have to back up the equivalent in Bank of England pounds). Jersey money is different, whilst they can be accepted, and are in certain cases, they tend not to be due to Jersey being a crown dependency rather than part of the UK. So, basically: they are legal tender in their country of issue (only Bank of England pounds are legal tender throughout), they are recognised currency throughout rest of UK and thus can be accepted, but only at the discretion of the seller (you can't shout at a bus driver for not accepting the money, if it isn't company policy to accept Scottish notes). Strange but true fact: in strict terms, no paper money is legal tender in Scots Law. Only the £1 note was, but it was withdrawn.
I remember whilst on a bus in Bristol, a guy came on with a Scottish fiver. The driver took one look at it, and simply said: 'f*** off'. Guy did a two minute rant at him. The driver then said: 'finished now? Good. F*** off' I nearly peed my pants watching that.