The charity Action on Elder Abuse believes 5% of older people - some five million people - have been abused.

It estimates from calls to its helpline that about 10,000 to15,000 have been sexually abused.

Ginny Jenkins, the charity's director, told its national conference on Thursday that the first step to tackling the problem was to acknowledge its existence so that victims could talk about it:

She said: "The idea that someone could rape or indecently assault a frail elderly person is so shocking that people often prefer not to think about it at all.

"But sadly it happens far more than anyone would like to believe.

"As a society, we have faced up to the appalling facts about abuse of children and people with learning difficulties and now we must begin to open our eyes to the reality that some people target and abuse vulnerable elderly people."

National register

Wendy Greengross, a patron of the charity, said another problem was that elderly people may not feel comfortable talking sexual matters.

She added that, as with all forms of sexual abuse, some might think they were partly responsible for their abuse.

Ms Jenkins told BBC News Online that there was a lack of appropriate services to support elderly people who had been abused.

She said social services and women's aid organisations were not geared up to deal with it.

"Social services tends to concentrate on child protection. It may be right for the nation to look to children as the nation's future," she said.

"But in terms of each individual member of the nation we should be looking to older people as they are our own future."

Action on Elder Abuse, set up six years ago, supports proposals in the government's Social Services Bill to create a national register to be created for all staff working in the social care field, including those working in old people's and nursing homes and community care services for the elderly.

Ms Jenkins said that there was currently nothing to stop care staff who had abused elderly people moving from care home to care home.

Learning difficulties

The conference also heard from Tom Burgner, who headed an inquiry into the sexual abuse of people with learning difficulties.

He called for much tighter regulation of residential and nursing homes for elderly people.

He said: "It is far easier not to give permission to set up an establishment than to close it down afterwards."

He also called for elderly people to be offered the same protection as children in care and for prison sentences for those found guilty of abusing the elderly to be increased.