Manu Tuilagi is at the centre of a transfer tug-of-war that is threatening to blow Premier Rugby's uneasy salary cap investigation impasse wide open.

The Leicester Tigers and England centre, currently side-lined by a long-term groin injury, is understood to be the subject of a £400,000-a-year offer from Aviva Premiership rivals Saracens which has infuriated the east Midlands club and could see the salary cap investigation reopened.

According to one well-placed source, relations between England's top Premiership clubs are understood to be 'close to breaking point' with Saracens and Bath – last season's Premiership finalists - understood to have made significant concessions in a bid to avoid points deductions and even financial sanctions for historic breaches of the cap.

Leicester Tigers and England centre Manu Tuilagi is at the centre of a transfer tug-of-war

Tuilagi (right) is understood to be subject of a £400,000-a-year offer from Leicester's league rivals Saracens

Premier Rugby opened an investigation into the two clubs in December last year, with Northampton also now believed to be under scrutiny, following claims they were in breach of strict guidelines governing the amount clubs spend on player wages aimed at ensuring the league remains competitive.

But the investigation was shelved in April after rival clubs agreed to a number of concessions, some regarding player transfer targets, leaving opposing fans exasperated at the league's failure to punish the two clubs with the deepest pockets in English rugby.

Leicester, whose relationship with Saracens has deteriorated since the departure of former Allianz Park chief executive Edward Griffiths last March, initially agreed to the investigation being shelved on the understanding last season's Premiership winners would withdraw their interest in Tuilagi, who is out of contract at the end of the upcoming season.

But the north London club, backed by a consortium of millionaire South African businessmen, have maintained their interest in the Samoan-born star, who was not considered for England's World Cup campaign after pleading guilty to assaulting a police officer in April.

Saracens are backed by a consortium of millionaire South African businessmen who still want Tuilagi

Sportsmail understands Saracens' refusal to retract their interest in the injury-plagued 24-year-old - who when fit is one of the world's best centres - led to heated exchanges at last Wednesday's pre-season meeting of Premiership stakeholders with Leicester chief executive Simon Cohen furious at their rivals continued interest in Tuilagi.

Saracens and Bath allege the salary cap, which has been raised to £5.5million this season, is a direct breach of European trade laws and have threatened legal action if action is taken against them over historic breeches.

The level of sanctions available for salary cap breeches range from four points for a minor breach to 40 points for a breach in excess of £250,000. Premier Rugby bosses had hoped to bury the findings of their investigation, which were twice postponed last season, after brokering the uneasy truce.

But those hopes now appear ill-founded, with Tuilagi at the centre of the row.

'There's so much horse-trading going on it's like a scene out of West Wing,' one well-placed source said.