Workers at one of the country's biggest rail firms are to be balloted for strikes over pay, it was learned today.

Members of the Rail Maritime and Transport Union at South West Trains will be asked whether they want to stage walkouts in protest at a deal worth up to four per cent.

The offer has been rejected by union negotiators and the RMT executive has now decided to ballot more than 2,000 guards and clerical staff.

Phil Bialyk, the union's regional organiser, claimed that SWT was offering a better deal to its drivers.

A spokesman for SWT said: "We are very surprised to learn that the RMT is talking about strike action as we consider that the negotiating process is still ongoing and we have by no means exhausted this process."

SWT - which operates services between London and southern and south-west England, including some services in Sussex - said it had offered the same deal to the RMT as to the driver's union Aslef.