British Government refuses to accept their own currency

They rewrote the law for the IRS. They minimum you can pay them with now, is a one dollar bill. They are required to take "Tender" not "coinage".
Edit: in direct response to being paid in loose change.

And yes. I know what this says, but the IRS is not required to accept payment in coinage.

"legal tender
noun
: money that the law allows people to use for paying debts
Full Definition
: money that is legally valid for the payment of debts and that must be accepted for that purpose when offered
Examples
Soon after France adopted the euro, the French franc ceased to be legal tender.
coins and bills are considered legal tender, but postage stamps are not
First use: 1739"
Merriam Webster's dictionary.