Thatcher instigated a load of reforms that were necessary because the country was in a shit state (maybe 10 years more of what we are doing at the moment will lead to the same).
Blair rode the back of that and rather than moderating the Thatcher reforms where necessary instead rode off the back of them. This helped contribute to the credit boom and the GFC in 2008.
The Tories were pretty much forced to implement austerity after 2008 to deal with the consequences of the credit boom. This was going OK until COVID. At which point they bunged the middle class a massive pile more money than they needed to (amongst other things) and wrecked the borrowing figures such that we can't borrow any more money.
Labour took over from the Tories on a stupid promise not to fiddle around with taxation, but to make things wonderful again. Unfortunately the also inherited the ability not to borrow any more money. So they are now stuffed. They probably need to tax wealth more and productivity (wages) less, but haven't got the guts to actually do it.
Brexit continues to be a big fat nothing burger. Looking at the stats the UK economy hasn't fared much different than other comparable economies in the G20, and it is hard to separate out the effect of COVID which has been more dominant. There are people out there that claim that if the UK hadn't left the EU we would be outperforming all the equivalent G20 economies now by a significant margin and everything would be sunny and wonderful. I remain to be convinced.
Importing a ton of people that don't add significantly to the GDP figures hasn't helped (GDP per capita is lowered if you bring in people who aren't contributing significantly to GDP). This is probably another part of the story though.
The above is largely the history of the past 40 years minus the party spin and politics.