I'm not sure how you reached that conclusion.
It's true that 'activity' was booming, and there was pretty much full employment, but it was all on borrowed money. Economically at the end of WW2, Britain was bankrupt, but there were totally unrealistic sky-high expectations that it would become a 'land fit for heroes'.
I was born in June 1939, so I lived through the post-war era. It was characterised by demarcation disputes, low productivity, adversarial labour relations, leading to lack of capital investment, an overly large public sector, decline in heavy industry, strikes in the labour-intensive car industry, turning out poor quality cars on machinery which was clapped-out during the war years. During the 'winter of discontent' 1978/79, rubbish piled up in rat-infested streets and bodies went unburied.
Harold Wilson (1974-76) was elected on a slogan of ‘13 years of Tory Misrule’ (Sounds familiar!).
His record as prime minister was soon seen as one of failure, that sense of failure was powerfully reinforced by Jim Callaghan's term as premier (1976-79). Labour seemed incapable of positive achievements. Unable to control inflation, unable to control the unions, unable to solve the Irish problem, unable to solve the Rhodesian question, unable to secure proposals for Welsh and Scottish devolution, unable to reach a working relationship with the Common Market, unable even to maintain itself in power until it could arrange a general election on the date of its own choosing.
The Unions rejected continued pay restraint and in a succession of strikes over the winter of 1978/79 (Winter of Discontent), secured higher pay, although it had virtually paralysed the country, tarnished Britain's political reputation, seeing the Conservatives surge ahead in the opinion polls.
"The Day That Britain Went Bust" - December 15 1976:
When Labour Chancellor Denis Healey went cap in hand with his begging bowl to the International Monetary Fund to bail out Britain.
https://www.chathamhouse.org/public...2016-12/britains-big-bailout-december-15-1976
It was little wonder, therefore, that Margaret Thatcher resoundingly defeated Labour in 1979.
The fall of James Callaghan in the summer of 1979 meant, according to most commentators across the political spectrum, the end of an '
ancien régime', a system of corporatism, Keynesian spending programmes, subsidized welfare, and trade union power.
During World War II the government was forced to borrow heavily in order to finance war with the Axis Powers. By the end of the conflict Britain's debt exceeded 200% of GDP, as it had done after the end of the Napoleonic Wars. As during World War I, the US again provided the major source of funds, this time via low-interest loans and also through the Lend Lease Act.
By the end of World War II Britain had amassed an immense debt of £21 billion. Much of this was held in foreign hands, with around £3.4 billion being owed overseas (mainly to creditors in the United States), a sum which represented around one third of annual GDP.
At the end of the war Britain Lend Lease was ended but Britain needed to continue to make payments for Lend Lease and import food but with industrial production turned over to wartime needs there was little export sales to cover the costs. In 1946 Britain took a loan for $586 million (about £145 million at 1945 exchange rates), and in addition a further $3.7 billion line of credit (about £930m at 1945 exchange rates). To the total loan of $US3.75bn, Canada contributed another US$1.19 bn, both at the rate of 2% annual interest. The debt was to be paid off in 50 annual repayments commencing in 1950. However, some of these loans were only paid off in the early 21st century.
It took until 31 December 2006 that Britain made a final payments of $83m (£45.5m) to the US & $23.6m to Canada.
The Tories haven't covered themselves with glory this last few years, but looking back over my long life, every time that Labour have been given the keys to the car, they've crashed it. That's why they've spent so many years in opposition as little more than an angry 'protest group'. Too much 'welfare' rather than 'workfare' keeps people in poverty. Labour are more obsessed with redistributing wealth than creating it.