I agree "economic devastation" is an emotive term, and which should be defined, but without having access to detailed economic web-sites to which to link, may I start with 'increasing health and wealth inequalities', caused by Osborne's austerity. I would suggest, from partial memories of articles in Private Eye primarily, this was caused by an under-regulated financial network imploding. The consequences for the majority of the population, coupled with an inept governing elite who under-performed after this global financial crash compared to other equivalent nations, has been pretty 'devastating', when incomes have stagnated at best (mine in the public sector has decreased by 25% in real terms), and things have not improved with Brexit and Covid.
Yes, we all have the opium now of colour televisions, buying tat on the internet, etc., compared to the 1930's, but compared to other nations, I think things could be much better for the U.K. population. Sorry I do not have the time (or ability!) to write a cogent definition, but perhaps someone else can supplement this concept with other suggestions and evidence. My point I was trying to make was, more than one certain party can mess up the economy, and it is not just govt. Other agencies conribute to the mess, but the tax-payer usually foots the bill.
As to 'where to get the money', I would suggest expanding the fiscal net: again banks, multi-nationals, monopoly public suppliers, and many others, have had their taxes reduced over the years. At least I think this is the case, if I remember Private Eye correctly. 🙂