UNION chiefs last night rejected a plea to involve the arbitration service Acas in the long-running conductors dispute at Arriva Trains Northern.

The North-East Rail Passengers Committee said it could not see how a breakthrough in the pay row could be made without mediation from a third party such as Acas.

The passenger watchdog said it was concerned and dismayed because no formal talks between Arriva management and unions had taken place for at least five months.

Last night Stan Herschel, regional organiser with the Rail Maritime and Transport union (RMT), said both sides were simply too far apart to involve Acas.

He said: "We have constantly shifted our position and have already hit the bottom line.

"Our conductors have been offered four per cent when nine per cent would be a more realistic offer. I know what my members expect and their aspirations and the ball is firmly in Arriva's court to narrow the gap."

The North-East RPC has become increasingly exasperated by the stand-off in the conductors dispute which has lasted for several months.

It urged both sides to put their past differences behind them and to end the "continuing strike misery".

In a statement it said: "Despite the apparent width of the gulf separating Arriva and the RMT we urge both parties on behalf of all passengers to draw a line underneath what has gone and renew their efforts, without precondition, to find a way forward."

Conductors have held a series of strikes in recent months crippling services in the region.

Further strike dates have been announced running up to and including Christmas Eve and New Year's Eve.

Ray Price, Arriva Trains Northern's managing director, said: "We are pleased that the North-East Rail Passenger Council shares our view on the role the Arbitration, Conciliation and Advice Service (Acas) could play.

"We have repeatedly asked the RMT to attend a meeting with Acas and we certainly hope that the union will now respond positively to our open invitation."