[NLips]

Note that legal tender != can buy milk with. Legal tender is only about payment of debt. A shop selling you something doesn’t have to accept any specific form of payment, as they don’t let you build up a tab which needs repaying.

[LBJsPNS]

Were I a shopkeeper and someone offered me a £1 Sovereign for £1 worth of merchandise, I don't think I would have any trouble accepting it.

[freeone3000]

The Coinage Act of 1971 describes, in detail, which combinations of coins must be accepted for various purchase amounts.

[Symbiote]

No, it specifies amounts for legal tender. That's relevant when paying a debt, but not making a purchase in a shop.