Northampton believe the Guinness Premiership salary cap of £4m a year is unlikely to survive after the end of next season as teams seek to rival French clubs, some of whom are spending three times that amount on their squads.

The Saints' chief executive, Allan Robson, said: "I believe it is inevitable the cap will go. We have agreed that there will be no change this season or next but expenditure is growing and we are competing with overseas sides. Northampton and Leicester are two big clubs in terms of finance and structure, but if you look at the budgets of big French clubs, it is nothing. Competitive balance on the pitch is important to our domestic game, but I am raising the issue about competition outside that which demands higher budgets."

Mark McCafferty, the chief executive of Premier Rugby, said a review of the cap would be conducted at the beginning of next season. "The most important thing for us as an organisation is that the Premiership remains an unpredictable tournament," he said. "We do not want the same sides finishing in the top four every year. We are competitive in Europe, as we have shown in recent years. If that changed, we would have to rethink the cap."

The cap rose significantly in the summer and not every club is spending £4m on wages. "We are currently awaiting figures, but I think most sides will be spending close to the limit," said McCafferty. "As resources develop, the cap will rise; equally, if they decline, it will decrease."

Premier Rugby and the Rugby Football Union have joined forces to analyse the impact of the experimental law variations before a vote is taken by the International Rugby Board next March to make them permanent. "We want objective evidence to base a decision on," McCafferty said.