A mother sensationally accused of forging her ex-boyfriend’s signature to conceive a child using IVF treatment has been ordered to pay an estimated £120,000 in legal fees.

In an extraordinary High Court case, which concluded last week, the child’s father failed in his unprecedented bid to sue top fertility clinic IVF Hammersmith for failing to check he consented to the procedure.

The man, a multimillionaire property developer, had claimed his former partner ‘tricked’ the private Harley Street clinic into implanting the embryo, which they had frozen following previous IVF treatment when they were still a couple, and sought £1million towards the cost of raising his unwanted daughter, now six.

The Mail on Sunday understands the child’s mother, known only as R, strenuously denies forging her partner’s signature on the paperwork. The court also heard the father, ARB, attended fertility appointments in early 2010, the same year R became pregnant, in which the possibility of a second child was discussed.

In the extraordinary High Court case, which concluded last week, the child’s father failed in his unprecedented bid to sue top fertility clinic IVF Hammersmith (pictured) for failing to check he consented to the procedure

Despite this, a controversial decision by the judge, Mr Justice Jay, means R must pay a significant proportion of IVF Hammersmith’s enormous legal bill because of her alleged ‘deplorable conduct’.

It comes even though she was only brought into the case as a third party by IVF Hammersmith after she agreed to help them defend the action ‘in any way she could’, a source said.

But she now faces losing the home she shares with the two children in order to pay the fees.

R’s barrister, Mark McDonald QC, told The Mail on Sunday: ‘This is a tragic case where the real victims are the two children.

‘My client is a wonderful, caring mother and it is regrettable that one day they will undoubtedly read the evidence of the father who described his child as an ‘alien’ in his family.

‘Mr Justice Jay described the father’s evidence in part as self-indulgent and was saddened when he heard what he said about the child.

‘The likely result of this case is that the mother will lose her home, the home she has built for herself and the two children.’

The man (pictured left and right), a multimillionaire property developer, had claimed his former partner ‘tricked’ the private Harley Street clinic into implanting the embryo, which they had frozen following previous IVF treatment when they were still a couple

The woman’s solicitor, Richard Harrington at Axiom Stone, said the costs order ‘confirms that the court is arguably punishing our client for her conduct even though the claimant lost his case’.

‘The judge further decided that the clinic’s conduct in adding our client as a defendant was acceptable despite his comments at trial that the clinic only added her as a tactical move to put pressure on the claimant.’

Mr Harrington also revealed the father refused an offer from the clinic to settle the dispute in advance of the trial, despite the likelihood that he would lose.

In his reasoning document, which accompanies the costs order, Mr Justice Jay (pictured) wrote: ‘The conduct of R has been deplorable. I agree with [the father’s barrister] Mr Mylonas that she has systematically perjured herself'

He said that meant R ‘effectively pays a large proportion of legal costs for the claimant to have his day in court. That situation appears to be quite perverse.’

The father was ordered to pay 60 per cent of the clinic’s legal fees in defending the case, which is also likely to run into six figures.

In his reasoning document, which accompanies the costs order, Mr Justice Jay wrote: ‘The conduct of R has been deplorable. I agree with [the father’s barrister] Mr Mylonas that she has systematically perjured herself.

‘The only reason I am not referring my Judgement to the CPS is to protect the children.’

The couple met in 2004 and, despite a volatile relationship, conceived a son via IVF in 2008. They separated in 2010, but the court heard R believed their relationship had improved towards the end of that year.

But on Valentine’s Day 2011 R sent ARB a text to say she was pregnant, and that he had signed the relevant forms.

The clinic’s terms and conditions state that any changes to personal circumstances, or consent to treatment, must be declared.