More than two in five (41%) working carers would not have a job if flexible working was not available, research from Phoenix Group found.
This was higher than the figure for the general working population, which stood at 31%.
Nearly two thirds (65%) of working carers said they would look for a new job if their employer restricted flexible hours.
The 2021 Census put the number of unpaid carers at 5 million in England and Wales, and 0.8 million in Scotland.
Over half (55%) of working carers said they would start looking for another job if their employer ended working from home policies.
This compares to 47% of all workers, highlighting a higher reliance on flexible options among carers.
Carers UK estimated that over 600 carers leave work every day to care for older or disabled relatives.
Analysis by Phoenix Insights showed that 47% of carers aged 60 to 65 had no private pension savings.
Those carers who did have pension savings had 17% less than the UK average, with a gap close to £37,000.
Claire Hawkins, director of corporate affairs and brand at Phoenix Group and executive sponsor of Phoenix Group’s colleague Carers Network, said: “For millions of people, balancing paid work and caring for a loved one is a challenging reality.
“Too many carers are put in the unenviable position of having to choose between staying in work or caring for a loved one.
“That’s why it’s so important for businesses, who can benefit hugely from carers’ skills and experience, to recognise the need to enable them to work flexibly.”
Hawkins added: “Better access to flexible work, and the provision of paid carer’s leave, is crucial in enabling carers to remain in work for as long as they want to, so they can earn and save enough for their future.”
More than a third (37%) of working carers had a flexible work request turned down, compared to 20% of all workers.
62% of carers said they could not meet their caring responsibilities without flexible work.
A further 62% said they were more productive working at home and 68% said flexible hours made them more productive.
Previous research by Phoenix Insights found 59% of full-time working carers would return to work or increase their hours if given the right support.
Almost four fifths (71%) of working carers said the government should make the right to flexible work mandatory for all employees, compared to 62% of all workers.
Helen Walker, chief executive of Carers UK, said: “Having a carer-friendly employer with great flexible working can be a game-changer for unpaid carers, helping them to juggle work and unpaid care for disabled, older or ill relatives or friends.
“Staying in work helps avoid financial hardship in the short and longer term. It’s a win-win for carers and for employers who retain talent, which is good for productivity and for the economy.”
Kirsty McHugh, chief executive of Carers Trust, said: “This vital research by Phoenix shows how employer support for carers can have a huge impact.
“Carers have a wealth of skills and experience that employers can benefit from. Sadly, too many are left with no choice but to cut back their hours or leave the workforce altogether because of their caring responsibilities.
“This not only limits their career growth but also means businesses miss out on dedicated, talented staff.”
McHugh added: “The good news is, there are solutions. For those in work, flexible working and paid carers leave are absolutely crucial.
“For those out of work, specialist support from organisations who truly understand the challenges of caring is absolutely vital.
“Generic employment support does not work for unpaid carers – they need dedicated, specialist services.”