If you owe a ton, they'll take a cheque in any currency. But it costs them $50+ per cheque to process, so they'll be mighty cheezed off if you pay a $100 tax bill with a foreign currency cheque.
There are two ways they prefer you to pay:
1) Your UK bank can issue a draft in dollars. It still costs them $50+ to process it, but at least it's in dollars.
2) A freind, relative or other stateside person with a dollar checking account can write a cheque on their account. You'd have to pay your friend back, of course.
The IRS prefers a US dollar cheque written on a US bank account, so option 2 is better than option 1.