The Bank of England, was at first a private entity (established in 1688) and was only nationalized in 1946[1]. The notes they issued were backed by deposits of coin, gold, or silver. They broke with the gold standard in 1931, and it's then we see money tied not to a specific asset, but rather as a debt instrument; it's valuable only because someone promises to pay you back.
When the debtor is a nation-state, we have fiat money, and the money is backed only by the faith and credit of the nation who issues it.
As Weatherford's book points out, fiat currency was not invented by the British, as the Chinese were using a similar system in the 1st or 2nd century, and continued to use a paper money system until 1399. Abuses destroyed the value of the paper currency, and it did not reappear in China until the 20th century.