A Royal Mail strike across London could be on the cards for Christmas after the Communication Workers Union agreed to ballot its 30,000 Royal Mail members in a dispute over London weighting.

A spokesman for the Union said: "Against a background of soaring increases in housing and travel costs, council tax rises and fuel bills, our members have been offered a 47p per week increase in London allowances. Members have since unanimously agreed and are determined to achieve an acceptable increase."

A consultative ballot will be held within the next few days. The union said it expected a repeat result of the 2003 ballot when London postal workers voted for action over the same issue.

A ballot for industrial action will follow the consultation and the union said the results would be known by the middle of December.

The union spokesman added: "We are trying to avoid a dispute but unless Royal Mail improves its offer the capital will face serious disruption to services over Christmas."