Rugby is heading to the law courts for the second time in less than a year with the Rugby Football Union and Premier Rugby refusing to concede any ground in their dispute over the Heineken Cup.

The 12 Guinness Premiership clubs have voted to withdraw from the competition if their French counterparts carry out a threat to boycott the tournament, with their decision expected tomorrow.

Concern about the RFU's refusal to hand over share and voting rights - plus anxiety over fixture congestion next season, which starts with the Rugby World Cup - are behind the French stance.

The day began with RFU management board chairman Martyn Thomas insisting the clubs are contracted to participate in the Heineken Cup and he confirmed Twickenham would pursue legal action against them if they refuse.

Asked whether the RFU would have to sue PRL, Thomas said: ''Regrettably that would be the case."

However, a statement released later suggested a softening of the RFU position with Thomas saying legal action would be ''carefully considered'' following any boycott.

It is understood a withdrawal would cost PRL £5m in lost revenue and the English clubs' umbrella organisation has already indicated it will seek to recoup the money by staging games against French clubs.

But Thomas declared that playing matches that had not been sanctioned by the RFU or the International Rugby Board would result in legal action.

He said: ''If PRL and the French clubs do decide to withdraw from the Heineken Cup next year then we will consider our position.

''The English clubs are legally bound under the 'Long Form Agreement' to play in the next two years of the Heineken Cup."