Britain performed worse than most other developed nations in its response to the Covid pandemic, according to an Observer analysis of international data, five years on from the first lockdown.

The UK spent more money than most other countries on economic help yet still ended up with larger drops in life expectancy, more people too sick to work, huge levels of homelessness and soaring mental health problems among young people.

Thousands will gather around the UK on Sunday to mark the fifth anniversary of the pandemic, yet the effects of Covid are not over and continue to affect the poorest more than others, health and civil society leaders warned.

“We haven’t seen the bounceback that other countries have,” said Siva Anandaciva, director of policy at the King’s Fund thinktank.

“When I look at the one big global indicator of how healthy we are, which is our life expectancy, we’ve gone backwards.

“We’ve fallen back to levels of a decade ago, while other countries have kept motoring on in western Europe and leaving us behind. It’s a pretty damning indictment of what happened.”

Hetan Shah, chief executive of the British Academy, said inequality was “the primary story of the pandemic”. “You still find that people from poorer backgrounds are more likely to have been impacted,” Shah said, adding that the rate of long Covid in the most deprived households is double that of the most wealthy.

“One of the dreadful things about the pandemic was that, as a side-effect, there was less money to invest in public services across the piece. The worry is that some of the trends we’re seeing, unless there’s active work to stop them, will continue.”

The UK spent 19.3% of gross domestic product on extra spending and forgone revenue, and gave loans worth a further 16.7%, according to the International Monetary Fund – more than almost every other developed country except Japan, Germany and Italy.

Yet the return on this investment was poor. After the lockdowns ended, every other G7 nation except the US saw more adults rejoining the workforce. However, the UK, which has historically had a better than average number of people in work, saw the reverse.

There has been a 0.5% increase in the number of people not working and classed as economically inactive, with about 2.7 million too sick to work.

In life expectancy, one of the most fundamental measures of how a country is able to look after its people, the UK is in a worse position than most other developed countries.

Women can expect to live to 82 years and 10 months, about three years less than in Spain, Australia or Italy, while men can expect to reach 79, about two years less than in the same countries, reversing more than a decade of lifespan increases.

OECD (Organisation for Economic Co-operation and Development) figures show that, in similar countries, homelessness is static or has been falling, but it has more than doubled in England since 2010. About 45 out of every 10,000 people are either sleeping rough or in temporary accommodation.

Children are also significantly unhappier. The Education Policy Institute said the OECD figures showed that the UK now has the “second lowest average life satisfaction of 15-year-olds across all OECD countries”.

Half of pupils in England (48%) rated their overall life satisfaction as seven or more out of 10, compared with 61% across other countries.

And the UK has the sixth highest number of Covid deaths reported to the World Health Organization, with 232,000 fatalities, although Britain’s excess mortality rate is nevertheless in line with other nations, according to the scientific publication Our World in Data.

While international comparisons can be confounded by different methods of measurement, the main difference between the UK and other developed countries is that the NHS had been consistently underfunded, health experts said.

Anandaciva said he had asked a German counterpart shortly after the first lockdown how Germany was dealing with hospital backlogs. “He paused and said: ‘What are you talking about?’ And it became clear that they had got back on track and the reason was that they were never overwhelmed. They had the capacity, the beds, the staff, not only to cope with the pandemic but also get things back to normal quicker.”

Paul Johnson, director of the Institute for Fiscal Studies, said: “Broadly speaking, we actually spent more and borrowed more than almost any other country. We were in that sense particularly generous – we increased our borrowing and debt by more than most other countries over that period.”

He added that the increase in people who are economically inactive because of illness was also a problem that affected the UK and few other countries. An extra 1 million people are claiming disability benefits and 700,000 more are claiming incapacity benefits since before the pandemic.

“Denmark has seen a small increase, but no other major country has seen an increase or any shift from its prior, pre-Covid trend,” Johnson said.

“We’ve seen this unbelievable increase in numbers, which we don’t really understand, and we don’t know whether it’s associated with Covid, but it’s certainly coincident with the period after it.”

Mental health problems among children and young adults are also worsening, accounting for 45% of all diseases affecting 10- to 24-year-olds.

Sunday’s Day of Reflection will see a procession along the national Covid memorial wall by the Thames in London and services at St Paul’s Cathedral, Westminster Abbey and the National Memorial Arboretum in Staffordshire.

Later this week, the Covid inquiry will hear evidence from former ministers Michael Gove, Steve Barclay and Helen Whately on how the government went about procuring PPE, ventilators and oxygen in the first stages of the pandemic.