"What gets measured gets managed"

- Peter Drucker

The whole point of issuing your own digital currency is you have total control over that currency. A $20 bill used by a hooker to snort coke? You know that if it were a digital $20 bill, Charles Grassley and Lindsay Graham would introduce the "Accountability in Spending Somehow Happens to Overwhelm Liberties for Everyone Act" whereby any use of digital currency to purchase controlled substances compels the DEA to seize all of the indicted individual's currency in all banks and stores of measure to compensate for the expense of policing. So now the coke dealer is penniless, the hooker is penniless, the convenience store clerk is penniless and the soccer mom is penniless and Fox News either decries the downfall of humanity or trumpets the era of personal responsibility depending on who's in the White House that year.

India went "hey guess what your old cash is worthless come exchange it by Monday" because they basically wanted to shake down and control the gray economy. If it had worked they wouldn't be busily looking into shutting down crypto. This is why Morocco outlawed crypto in 2017 - so they'd have currency controls. Obviously it crippled Bitcoin. Meanwhile in Russia, which banned Bitcoin:

Kremlin Press Secretary Dmitry Peskov, said of the meeting “Putin and Buterin discussed the application of technologies in the country. And that Putin supported the idea of establishing new business relationships following the road paved by Blockchain technology.” Time quoted a Russian state owned bank executive, who was at the event, saying “This is how the whole thing started”, regarding the Petro project.

So the British could pursue a public, privacy-minded fork of a public blockchain but they won't. Because they do dumb shit like say cancer is covered by the NHS but dementia gets to bankrupt you.