I'm not convinced that the UK has been all that comparable to Germany and France for years. GDP is of course an imperfect measure of the real size and capacity of the economy - Ireland has about twice the GDP per capita of all of those countries, but there's not really any way for their government to capture that economic activity as funding for stuff - and certain other metrics are not so great. For example, the average UK household is apparently £8,800 a year worse off than in Germany or France (median income, adjusted for purchasing power) and that gap's been there since about 2008: https://www.theguardian.com/business/2022/jul/13/average-uk-...

In some sense, the UK became poorer than the other European countries it'd normally be compared to at the end of the previous New Labour government when the financial crisis hit and just never really recovered from that. It's possible there is no obvious way out anymore - everyone being poorer means less means less money for them to spend on consumer products and services and less tax revenue the government to spend on things like healthcare and infrastructure, and all of that means less businesses interested in setting up in the country (for reasons other than low taxes anyway) and less tax revenue, less well paying jobs... it's a vicious circle to be stuck in.

Even before that happened, the New Labour-era spending was obviously unsustainable at the level of tax they were willing to charge. Despite the economy booming and a bunch of NHS infrastructure spending being moved off government books via expensive PFI programs the national debt went up consistently as a proportion of GDP year after year. Afterwards the Tories made a big fancy show of austerity and cutting back on government spending (and to be fair it did eliminate the deficit like they promised, for a while anyway) but even their big scary austerity program only froze the proportion of GDP spent on healthcare for a while.