Looking at the graph, even though the FTSE100 is at an all time high, relative to money printed it's worth about 30% less than pre pandemic times.
Inflation is caused by excessive money printing and the UK is no different.
Inflation is indeed amonetary phenomenon, to re-hash Friedman. Unfortunately for this quote the world has more nuance:
The quantity of M2L excluding OFCs can work as a forward indicator to inflation, especially as it's more timely than CPI data. Sometimes. It depends what's happening to velocity too.
The 1980s showed the breakdown in causality between broader forms of money and inflation. To return to that policy would be a disaster.
But why would you compare it to a stock index? Stock is didcounted by interest rates. When rates change so does the discounting factor. That's only one problem with this apples to grapes comparison.
[1] https://www.bankofengland.co.uk/quarterly-bulletin/2014/q1/m...