Alienation can include a parent constantly badmouthing or belittling the other adult, limiting contact between the child and the targeted parent, forbidding discussion about them, creating the impression the parent does not love the child and forcing the child to reject the parent.

“It’s undoubtedly a form of neglect or child abuse in terms of the impact it can have,” said Mr Douglas. “I think the way you treat your children after a relationship has broken up is just as powerful a public health issue as smoking or drinking.”

She said her former partner made “false and fabricated allegations” against her in order to gain custody and “manipulate my son so deeply that he now has no memory of his loving childhood with me”.

Now her contact with the 14-year-old is limited to Skype conversations and visits once a month.

“If I had been sent to prison I would have been able to see my son more than I do now,” she said. “My son is brainwashed – he is emotionally dependent on his father and behaves as if he were in a cult. My son has no idea what is going on, only that he feels angry at me.

“The more parents who stand up to this and say it is unacceptable the better. Emotional abuse is just as horrible and controlling as physical abuse. It’s unacceptable and things need to change in the way it is dealt with.”

In some countries, governments have put in place legislation to prevent such behaviour. In Italy parents can be fined, whereas in Mexico, guilty adults can be given a 15-year jail term.

And in America “parenting coordinators” are ordered and supervised by the courts to help restore relationships between parents and children identified as “alienated”.

“But this is hardly ever the case because ultimately the punishment on the parent will rebound on the child.”

However, judges in the UK are starting to recognise parental alienation, which is leading to some children being removed from the offending parent.

“But this is fraught with difficulty,” said Mr Douglas. “It’s a rocky road and a difficult process.”

Joanna Abrahams, head of family law at Setfords Solicitors, is one of the country’s few specialists in parental alienation.

She said: “The amount of enquiries we are getting about this type of behaviour is growing all the time. At the moment we get about three calls a day about this – and that’s a lot.

“It’s always been there but people are now beginning to understand more about it and how harmful it can be. You can run into the tens of thousands on cases like these.

“The frustration when you can’t see your child takes over people’s entire lives. Some kind of legislation needs to be put in place but what that is I can’t say.

“Each case is of course very different and it’s not always that someone is doing this on purpose. It might be subconscious behaviour.”

“It’s in the embryonic stages at the moment but it would include myself, Cafcass social workers and mental health workers – a cross-range of experts with the hope of developing something.

“I think we need to all work together to have a more joined-up approach to this behaviour which can be so damaging.”