Leeds Rhinos have begun a High Court battle for hundreds of thousands of pounds in compensation over their former star Iestyn Harris's move to Bradford Bulls.

Barrister David Griffith-Jones QC, for Leeds, told Mr Justice Gray that Harris terminated his contract with the Rhinos in September 2001 to fulfil his ambition of playing for Wales in the Rugby Union World Cup.

The Oldham-born back, who qualified to play for the Principality through his father, duly appeared for Wales in the 2003 World Cup in Australia but then decided to return to rugby league.

He eventually joined the Bulls, but that left executives at Leeds Rhinos furious as they had included an option in Harris's termination contract giving them first refusal on his services in the event of any return. They are now suing both Mr Harris and the Bulls for allegedly breaching the contract.

But the player and his new club deny doing anything wrong and are expected to argue the contract is invalid and attempting to enforce it would be an unlawful "restraint of trade".

Jane Mulcahy, for Mr Harris, has already told the judge the option was sprung on the stand-off just days before he signed the rugby union contract and he had no wish to tie himself to Leeds.

Gary Hetherington, chief executive at Leeds Rhinos, was the first witness to take the stand and he insisted that right from the start of negotiations Mr Harris was made aware of Leeds' intention to sign him up on any return.

Harris was under contract in 2001 when he approached Mr Hetherington asking to be released so he could join rugby union club Cardiff Blues and play for the Welsh national side.

At the time he was the Rhinos best player, captaining them in his first full season after a record £350,000 move from Warrington.

After negotiations, Mr Hetherington agreed Harris could leave in return for massive compensation from the Welsh Rugby Football Union and the option agreement. But although Harris did go on to play for Wales 25 times, in 2004 he decided to return to league.

It was at that point Mr Hetherington believed Harris would honour the option and come back to Leeds. However Miss Mulcahy said it is Mr Harris's case that he did not believe he had to go back to Headingly.

"That, we disagree on," said Mr Hetherington, who said "right from the outset" it was made clear that the club wanted to employ Mr Harris should he ever return to league.

But Miss Mulcahy suggested the option was only thought of when the WRFU could not meet Mr Hetherington's request for £1million in compensation.

She put it to the Chief Executive that his compromise was £750,000 plus the option on Harris. "That's not true at all," replied Mr Hetherington. "I would have been happy not to have got any money at all and retained Iestyn Harris as a player."

Harris was offered £675,000 for a four-year deal with Leeds in 2004, but turned it down for a contract said to be worth £1 million with the Bulls.

Miss Mulcahy suggested Leeds' offer was not good enough because they had pledged to match Mr Harris's salary at Cardiff Blues, and he was on £200,000 a year. But Mr Hetherington said the club could have easily paid £200,000, and £675,000 was put on the table because Harris would be coming to the end of his career - and not worth as much - when it expired.

Leeds are suing for the loss of Mr Harris's services plus damages for missing out on increased ticket, sponsorship and replica shirt sales.

The case continues.