Yes, Tesco carries double cream. So does Sainsbury’s. And Harrod’s, of course – and most every other store in England, Scotland, Wales, and Ireland that sells groceries. But double cream, with a butterfat content of 48% is not produced in the United States. The best you can do here is heavy cream, which has a fat content of 36% to 40%.
Use heavy cream (perhaps a little more cream than the recipe calls for and cut back proportionally on some other liquid, if that seems practical) and hope for the best.
And calm down a little. At the rate you’re going you’ll probably curdle any cream you find….