Also, the usual argument that with metal-based currencies inflation is not possible is also false. There are several examples from history, which a primary one being when Mansa Musa passed through Egypt while making a pilgrimage to Mecca, he brought so much gold with him and gave it out so freely that it destabilized the economy. Spain also had similar inflation problems when they began mining silver in the new world. The supply far outstripped the ability to generate equivalent economic ability at the going rate which lead to inflation.
Gold (and silver) being used as currency has more to do with historical reasons than them being the best solution. It's sufficiently rare that you can't just create a bunch of it on your own, it's easy to work with so minting coins isn't prohibitively difficult, it doesn't corrode or react with most other common elements so it keeps up well, and it's not easy to counterfeit either, at least not since Archimedes. It also helps that they're shiny and you can make jewelry out of them so they are a good status symbol of wealth in and of themselves. Alternatively they'd suck to use for any real weapons so there was not alternative use in the past either outside of dishware and trinkets.
Fiat currency is perfectly fine. The problems are when the people who control the printing press get out of control. Money is just a commodity by which we easily facilitate trade so that we don't need to barter in all goods. Make more of any commodity and its value decreases according to supply and demand. If the UK wanted to fix the problem they could destroy some of the Pounds taken in as tax dollars. I'm generally surprised that governments don't do this more often, but I imagine it's because they couldn't explain to most people why they decided to "burn" $5 billion dollars instead of giving it to the poor or something like that.