The Lawn Tennis Association is conducting an investigation into its handling of allegations against a tennis coach jailed for having sex with an underage pupil.

Marc Lewis, of Farm Road, Edgware, was jailed on Friday for four-and-a-half years for arranging threesomes with his friends and the 15-year-old girl. Now the LTA are looking into past allegations against Lewis to see if he should have been prevented from teaching at the Temple Fortune Club in Bridge Lane, Golders Green, at an earlier date.

The victim's father, who cannot be identified for legal reasons, said: "The LTA had a number of previous complaints about the behaviour of Marc Lewis and in my opinion they failed to act appropriately."

The former Young Coach Of The Year was allowed to continue teaching adults at the club while he faced rape allegations by another student, a charge of which he was acquitted in June. It was only when the most recent allegations came to light that he was dismissed.

"With the benefit of hindsight we can see things differently," said Mike Berg, spokesman for the Temple Fortune Club, where Lewis even had sex with the 15-year-old girl in its committee room. "Marc had a lot of press at his time at the club about the positive way he was coaching juniors and it was difficult to see how such a highly-rated coach could be doing the things that he has now been found guilty of. There is a sense of shock around the club, and a sense of sadness.

"We will be talking about increased security at the club following this. It won't be allowed to happen again."

A spokeswoman for the LTA said: "We are conducting an investigation into the matter with the police and will not comment until we have reached a conclusion."

Lewis, 26, had been asked to give extra tennis lessons to the teenager by her father who had heard of his growing reputation as a top coach. He had sex with her on a number of occasions between December 2002 and March 2003. He also encouraged two friends, known as John and Jonny, to do the same, both at her home, while her parents were out, and at the Premier Lodge hotel in Edgware.

Sentencing at the Old Bailey, Judge Giles Forrester said: "I have no doubt, although you denied it, that you knew her age and you exploited the undoubted affection for you which she held."

As he was led away, the judge said: "That is what lawyers call a long term sentence and you richly deserve it."

Lewis then blew a kiss to his weeping girlfriend in the public gallery and said: 'I love you.' The teenage victim of the crime has suffered intense psychological trauma since the event and was commended for her bravery in taking to the stand.

Detective Inspector Lance Spring said: "For a girl of her age to relive those experiences in the witness box was exceptionally courageous. She has been through a lot in the past 18 months and she is to be commended."

The victim's father agreed: "Lesser characters would have given up but the thing that kept her going was that she would save other girls from a similar ordeal that she had to endure."