Mike Norman explains why in terms of the US debt but the same goes for the UK too; and, the same for Australia, Japan, Turkey, India, etc. It is the same for any country which has control over, and issues, its own currency.
Note that this doesn’t include the Eurozone countries. They are not in control. They are users of the Euro not issuers of the Euro. Countries which lose control of their currencies lose much or most of their independence. Most Eurozone countries do have debt problems and so would the UK if it had adopted the Euro. Not to mention much higher levels of unemployment.
Modern Monetary Theory: Real Economics 