A father is suing a London fertility clinic for £1million for the cost of raising his daughter, claiming it let his former partner secretly conceive the child after the couple split up.

The father said his ex tricked doctors at the Harley Street Clinic at Hammersmith Hospital into impregnating her - using a frozen egg fertilised by his sperm - in October 2010, five months after their 'volatile and rancorous' relationship 'irretrievably broke down.'

He is now bringing an unprecedented claim for breach of contract, demanding £1m for the cost of raising his daughter, now six, plus legal fees for a custody battle with her mother.

The seven-figure claim includes 'hundreds of thousands of pounds' for the girl's private education, plus funding for a nanny, ski holidays in Canada and an eight-seater Land Rover Discovery.

Giving evidence, the father told Mr Justice Robert Jay his former partner told him she had undergone IVF with his sperm on Valentine's Day, 2011.

A father, left, is suing the Harley Street Clinic, pictured, in London for £1million to cover the costs of raising his child after claiming it let his former partner, right, secretly conceive the child after the couple split up. The pair cannot be identified for legal reasons

He claims the clinic, pictured, is in breach of contract for performing IVF without his consent

The father, who cannot be named for legal reasons, alleges his former partner forged his signature on a form allowing the clinic to unfreeze his sperm and give her IVF (file picture)

The former couple, who are both in their 40s but who cannot be identified for legal reasons, previously had a son together using IVF.

More of their eggs and sperm were being held in cold storage at the west London clinic, run by IVF Hammersmith Limited, of Harley Street.

The father, who is now married to another woman, said that his ex 'forged his signature' on documentation to secure the release of the fertilised eggs without his say-so.

The mother gave birth to a daughter in 2011, who the father 'understandably loves' despite the circumstances in which he says she was conceived.

But he blames the clinic for implanting the embryo into his ex without his knowledge.

The father told the court he responded to the Valentine's Day email with 'That's clever - why would you do that? I'm truly amazed by what you have done.'

Denying that the fertility clinic were not told the couple had split until 18 months after the baby was born, he told the judge: 'I phoned the clinic on February 15 2011 to reveal all. I wanted to know what had gone on. I was in a terrible state.

'My response was, 'Oh my God, how could this happen?' I'd never agreed to get her pregnant.

'My head was exploding. Can you imagine something like this happening?', he asked Mr Justice Jay.

'I was in a new relationship with a woman I loved very dearly. I thought: "Oh my God, this is going to destroy this relationship."

'It turned my head upside down. I just couldn't function. It was just so overwhelming.'

Jeremy Hyam QC, for the clinic, cross-examining, challenged his claim that he knew nothing and didn't want a new baby.

'It's right you wanted to have another child...the joint decision was that you and she wanted to have another baby,' he said.

After 'the green light of the normal tests' revealed his ex was able to conceive again, 'you were happy and excited at the prospect of a further IVF baby,' Mr Hyam claimed.

The High Court, pictured, heard the father is claiming for the cash to cover costs of his daughter's schooling, holidays, nanny and a Land Rover Discovery

'You knew and understood and agreed...that if the tests were positive you would proceed with a view to another child,' the barrister added.

'No...that's not correct...that's not true,' the father replied.

He admitted he had paid for tests and attended appointments after the birth of their son to explore the possibility of the mother having another baby via IVF.

'But it was not an agreement to have another child,' he insisted.

Describing their relationship before the breakup, the father told the judge: 'It was volatile. It was more than volatile.

'It was a relationship which was in terminal decline and quite an unhappy environment. It was a catastrophe, you can't imagine the environment we were in. It was a terrible time.

'Foolishly we had a child, thinking it might make it a better relationship. I wouldn't be the first person to have a child for that reason. At that time it was unbelievably difficult for both of us.'

He said that he had attended appointments and signed documents, prior to the final 'permission to thaw' form he says was forged, in order to keep the peace between them.

But he insisted: 'This was not a conversation or decision to have another child. Ever.'

'I agreed in order to avoid another shouting match. Then - here - I had a child coming. How could this happen?' he added.

Mr Hyam told him: 'That is clearly not true. This was a consultation with a view to undergoing a frozen embryo cycle.

'Your ex-partner had the tests you paid for and she comes back after the tests and says, 'good news the tests have come back normal.'

The father insisted: 'It was no joyous moment. We were barely on speaking terms. She had asked me to move out of my own house. We were in separate bedrooms. It was a few words as we were passing.'

The presiding judge is Sir Robert Jay, pictured, who was counsel to the Leveson Inquiry

The father told the court that the couple split up after 'a final hideous weekend' at a holiday cottage.

But Mr Hyam insisted that 'there was no irretrievable breakdown' and that they were still essentially a couple for some time after that.

'You were going through a turbulent time, similar to the turbulent times you had before, and you were not in another relationship.'

'It was a volatile relationship. Throughout all that period, despite the unhappy relationship, you were still trying to conceive a child.

'You were not married to your ex-partner, but you were being treated together and you intended to become the legal father of any resulting children.

'Despite such discord that you could hardly speak to each other, you paid for the consultation.

'You knew all the background. You knew how much she wanted another child.

'You can change or withdraw your consent at any time, except when the sperm or embryos have already been used.

'It is the responsibility of the couple once a year to inform the senior embryologist if there is any change in their personal circumstances.

'You never varied or withdrew that consent until January 2012. How was the clinic to know that you had divorced or separated?

'They wouldn't have,' the father admitted.

But he insisted that he had 'absolutely no knowledge whatsoever' that his ex was planning to get pregnant or had conceived until the Valentine's Day bombshell, and had in no way given her his blessing.

The father said that looking after his daughter has placed on him 'a financial burden which is not offset by any benefits.'

But Jeremy Hyam QC, for the clinic, today told Mr Justice Jay at London's High Court that they are not to blame, and should not pay a penny.

He argued that even if the father's signature on the 'consent to thaw' form is found to be forged, the clinic should not have to cough up.

The barrister claimed that the father played a full part in the IVF process up to a matter of months before the final form was signed and had signed one form even after the couple had split.

Fertility medics were not informed that the couple had broken up until 18 months after the baby girl had been born, he said.

'We did not expect - nor are we to be faulted for not expecting - duplicity of this nature,' he added.

Michael Mylonas QC, for the father, who lived in a £1.3m house in north London, said in his statement of claim: 'In 2011 the claimant's ex-partner gave birth to their daughter after her mother had forged the claimant's signature in order to procure the thawing of one of their embryos.

'Written documentation signed by the former couple was supposed to put in place safeguards in relation to future treatment, including the thawing of embryos.

'In breach of those safeguards, the defendant allowed the embryo to be thawed and implanted.

'The claimant brings a claim for breach of contract. As a result of the breaches, the claimant has suffered loss and damage including the cost of litigating with his ex-partner for parental responsibility and the cost of bringing up a second child.'

Mr Mylonas says that, when both parents 'signed an agreement for cryopreservation' in 2008, and later when the father signed an extension to the agreement in 2010, he had felt protected by a 'safeguard' clause in the contract.

The clause stated: 'In the event of divorce or separation, the IVF unit will only thaw or replace embryos if both (parents) give written consent.'

Failure to honour that clause exactly amounted to a breach of contract for which the fertility clinic must now pay dearly, the barrister argued.

Mr Mylonas told Judge Sir Robert Jay: 'The obligation was to obtain his informedconsent and they did not do that.'

The judge responded: 'You are saying that, if he didn't sign the form, there's no evidence that he gave informed consent. It's as simple as that.'

The barrister added: 'This incident wasn't even reported to the Human Fertilisation and Embryology Authority (HFEA) because the clinic considered that it had done nothing wrong.

'The HFEA has never recorded it as an adverse event because it considers that the clinic did everything right.'

The father blames the clinic because he claims they implanted the embryo into his ex without his knowledge (file picture)

But Mr Mylonas added that 'an increasing number of women are desperate to conceive' and what happened was predictable.

And he told the judge: 'The HFEA has completely sidestepped its obligations here'.

Urging the judge to reject the claim, Mr Hyam said: 'Assuming that the signature has been forged and it wasn't his and his consent wasn't obtained, that doesn't disturb the fact that we took proper care to ascertain that his reasonable consent was obtained.'

Even if it was not his signature on the final 'consent to thaw' form, his 'informed written consent' had been obtained by then via a series of earlier meetings the father attended and documents he signed, the barrister claimed.

'That there was an absolute duty to procure his signature (on the final form) must be wrong, and that there was a duty of reasonable care must be right,' he argued.

Mark Donald, for the mother, who the court heard is 'a teacher at a very good school,' has yet to address the judge.

She denies having forged the father's signature, but is also the subject of a third party claim by the clinic, the court heard.

Comparing the situation to undergoing a heart operation, Mr Justice Jay told Mr Hyam: 'You sign a form when you undergo a procedure - after the risks are explained - so that it is clear you understand.

'You are seeking to go behind the document and say that there is in fact an underlying informed consent.'

The judge earlier told Mr Mylonas: 'Your client understandably loves his daughter...if the signature (on the form) was his, that is the end of this case.'

The average cost of raising a child to adulthood in the he UK has been recently calculated at £230,000.

The father's statement of claim states that he had spent £45,000 battling the mother in court over custody and contact by 2015.

The 10-day High Court case, with six barristers in attendance including two QCs, continues.