The Rail, Maritime and Transport (RMT) union is calling for the conductors to strike on 21, 23, 24 and 31 December as part of a long-running pay dispute.

Arriva says it will operate as many services as possible during the strike, helped by 180 conductors who have indicated they will not take part.

Ray Price, managing director of the train firm, said: "We are disappointed that the union has decided to hit what is undoubtedly one of the most important times in the year for so many people."

Conductors taking part in the dispute will lose at least �250 in wages, added Mr Price.

Stan Herschel, RMT regional officer, confirmed the strikes will go ahead, adding the union was keen to talk to Arriva "in a reasonable fashion".