Child sex abuse by women is significantly more widespread than previously realised, with experts estimating that there could be up to 64,000 female offenders in Britain.

Researchers from the Lucy Faithfull Foundation (LFF), a child protection charity that deals with British female sex offenders, said its studies confirmed that a "fair proportion" of child abusers were women. Donald Findlater, director of research and development, said results indicated that up to 20% of a conservative estimate of 320,000 suspected UK paedophiles were women.

The release of the figures comes days after a Plymouth nursery school worker, Vanessa George – together with Angela Allen from Nottingham and Colin Blanchard from Rochdale – pleaded guilty to sexually abusing young children.

Last night George's husband appealed to her to identify her victims, whom she has so far refused to name. Andrew George, 41, said: "I would plead to her, tell those parents, all those parents who want to know.

"If Vanessa has got any shred of human decency in her she should tell those parents." At her trial, Mr Justice John Royce had urged her to tell police the names of her victims.

Findlater said: "There was some suggestion it was only blokes that sexually abused children. Over time those arguments have fallen aside and people have had to wake up to the fact that actually, sadly, there is a fair proportion of women abusing as well."

There are 32,000 names on the sex offenders register. But LFF researchers suggest that the real number of paedophiles is 10 times this figure. Provisional studies suggest that between 5% and 20% are women.

The calculations put the number of female child-sex offenders in the UK at between 48,000 and 64,000, a figure Findlater describes as "highly possible". He said: "The problem is far bigger than conviction rates and, if you look at survivor studies, you end up with a very different story about the scale of the problem of female sexual abuse."

Detectives at Scotland Yard's paedophile unit, meanwhile, disclosed that they had detected an "increased prevalence" of female offenders. Metropolitan police sources said that quantifying the number of paedophiles in the UK was problematic, but there were likely to be hundreds of thousands.

Steve Lowe, director of Phoenix Forensic Consultants, which treats and assesses child sex abusers, said the true number of female paedophiles has remained hidden for too long.

"As a society, we find women sex offenders difficult to acknowledge. But those of us who work with paedophiles have seen evidence that women are capable of terrible crimes against children – just as bad as men." He said some female abusers remained hidden because they appeared before the family courts, where their cases were not publicised because of reporting restrictions.

The latest government figures, published six months ago, showed that 56 female child sex abusers were in custody, with 49 sentenced and seven on remand. Another 84 were under supervision in the community. Fewer than 2% of people on the sex offenders register are women.

Officials at the government's Child Exploitation and Online Protection Centre (CEOP) said under-reporting of incidents involving female abusers was a concern and warned that "copycat" abusers may attempt to replicate the abuse that took place at Plymouth's Little Ted's nursery, where George worked.

George, Allen and Blanchard, all 39, met through the networking site Facebook. Officials at the CEOP and at Scotland Yard believe that the internet is driving an increase in the number of sex abusers of children. However, while offences are on the rise, police say that they have detected no changes in the patterns of abuse that are carried out by paedophiles, whether men or women.