Councils in England are flouting the rules around "top-up" fees for care homes, according to an investigation.
Elderly people who have assets of less than £23,250 may qualify for financial support from their council to pay care home fees, but families can use their own cash to top this up so their loved one can enjoy extras, such as a nicer home or bigger room.
The law states that top-up fees should only be paid voluntarily. Councils should always offer at least one care home placement that does not involve the need to pay a top-up.
The charity Independent Age used freedom of information laws to find out whether councils were sticking to rules around top-ups.
It found that 35% of councils (36 out of 103) did not have a written agreement in place for families entering top-up fee arrangements.
Some 37% of councils (34 out of 93) also did not carry out annual reviews of the agreements, contrary to Government guidance on the issue.
Furthermore, 41% of councils (32 out of 78) said at least some top-ups in their area were arranged without the involvement of the local authority, contrary to the rules.
Estimates suggest almost 50,000 older people in England have a top-up arrangement in place for their care, which can run into hundreds of extra pounds a week.
In September, a report from the Local Government Ombudsman said families may still be due refunds over top-up fees.
It said councils failed to give families enough information or choice about care homes, with some breaking the law.
Janet Morrison, chief executive of Independent Age, said: "These new rules make it crystal clear that councils are responsible for ensuring that care homes cannot charge unfair fees to families for their relative's care.
"Councils must ensure that any additional top-up fees are reasonable, that there is a written agreement in place for them and that it is reviewed regularly.
"Yet our research shows that many councils are failing to do this and there is therefore a real risk that families are paying for care that should be free.
"This is an issue regularly raised on our helpline and families often say they feel pressurised into agreements, often at times of great worry and even if they're struggling financially themselves.
"Many are confused about the top-up fees they have been told they have to pay."
A Department of Health spokeswoman said: "Finding the right care home for a loved one can be a difficult and often confusing experience.
"Last year we strengthened the laws around this so councils have to provide families with at least one option that does not require them to top up and we expect all councils to follow these rules."