Families are having to settle for inadequate care home places because of "systemic failure" in the sector, a consumer group has warned.
The majority of people have limited choice and half of those needing care are having to wait for a bed, the survey by Which? found.
The watchdog found 48% of those who had arranged care for themselves or a loved one said there were no places in at least one of the local care homes they considered.
The lack of places meant many people were staying in, or moving loved ones into, care homes they were not satisfied with, with 17% saying they settled for a home they had reservations about.
A similar number (16%) ended up opting for a home away from friends and family.
When they did find a bed, as many as 25% of those who had arranged care said they were left feeling guilty or annoyed that they could not find a more suitable place.
Which? has launched a campaign calling for the Competition and Markets Authority's (CMA) inquiry into the care home market to go beyond immediate issues around quality, fees and complaints and "confront the creaking care sector now, recognising that the national picture masks huge differences in the number of care home places available at a local level".
Alex Hayman, Which? managing director of public markets, said: "Making the decision to move a loved one into a care home is difficult enough, so it is unacceptable that so many families are left feeling guilty or concerned about the choices they have made, simply because there is no choice.
"The CMA must look at the huge local disparities in care home provision, which are fast reaching crisis point."
Linda Thomas, vice chairwoman of the Local Government Association's community wellbeing board, said: "Councils are committed to ensuring that people have access to good quality care. But this is being put at risk by the severe funding pressures faced by social care services.
"An increasing number of care homes are closing and care providers are handing back their council contracts because of cost pressures. We have warned that £1.3 billion is needed right now just to stabilise the perilously fragile care provider market."
"It is vital that the Government sets out in the Autumn Budget how it will address the immediate social care crisis and deliver long-lasting reform that meets the needs of adults of all ages needing social care."
:: Populus surveyed 764 UK adults online who have arranged care in the last 12 months between September 14-20.
Janet Morrison, chief executive of the charity Independent Age, said: "It is simply not acceptable that nearly one in five people surveyed have reservations about their care home. This could be the tip of the iceberg, as this research looks at people who arrange care themselves or for a loved one.
"It poses questions about the quality of choice on offer for people making do with a care home the local authority have arranged for them.
"The Government must urgently publish their long-promised Green Paper on social care, and get on with delivering a social care system that meets the needs of older people now and in the future."