Cash Law

Extract from an articel on the law.

There is no legal right to demand change. This is nothing to do with any question of legal tender, in fact it simply relates to the old Common Law rule that when I owe you, say £5.55, I am under the duty to hand over exactly that sum. It is for me to find notes or coins of the correct denomination - not you, my creditor. This is surley only logical.
Similarly, although I can , for instance , pay a £4 debt with exactly £4 worth of 50p, 10p, or 5P coins, the principle does not work the other way. Those stories about being able to insist on a bus conductor having to accept a £10 note for a 10p ticket are hogwash. He would perfectly withing his rights in refusing to give you change and unless you give him 10p in coins, in asking you to get off the bus.
The reason is that coins or banknotes are legal tender up to a certain amount. They are never legal tender down to a certain amount, if you see what I mean.