LONDON (Reuters) - Prime Minister Theresa May criticized a wave of strikes sweeping Britain as unacceptable action that showed "contempt" for ordinary people in the run-up to Christmas.


Among planned strikes this month are walkouts by airline cabin staff, baggage handlers, rail conductors and Post Office counter workers.


"If these strikes share one thing in common, it's a shared contempt for ordinary people who are just trying to go about their daily lives," May's spokesman said on Monday, adding that parties should negotiate to avoid action.


He said the government would not rule anything out in terms of changing legislation to make striking more difficult.


British Airways (BA) said on Monday it would not be cancelling flights on Dec. 25 and 26 as the airline, owned by International Airlines Group, holds talks at the conciliation service Acas with the Unite union in an attempt to avert walkouts by more than 2,500 cabin staff.


"We have been working on detailed contingency plans to ensure that we are able to operate our normal flight program from all our airports on both Christmas Day and Boxing Day," BA chief executive Alex Cruz said.

The BA strike over a pay dispute is being staged by members of the airline's "Mixed Fleet", Unite has said, referring to cabin crew staff who have joined the airline since 2010. They make up about 15 percent of BA's 16,000 cabin crew.

Unite also said over 1,500 check-in staff, baggage handlers and cargo crew at airports across Britain will walk out for 48 hours from Friday in a long-running pay dispute.

Conductors on the Southern railway line were also taking strike action on Monday and Tuesday, the latest of over a dozen walkouts during a long-running dispute over whose job it is to open and close train doors.

Meanwhile post office counter workers on Monday began a two-day strike over job security and pensions, during one of the busiest weeks of their year.

The action will affect almost 300 Crown Post Offices, the larger branches usually found on high streets, but the rest of the Post Office's network of 11,600 local branches, and Royal Mail's delivery services, are not involved.

Elsewhere, staff at cereal manufacturer Weetabix voted on Monday for industrial action in the New Year over proposed shift changes.

(Reporting by Sarah Young and Michael Holden, additional reporting by Elizabeth Piper; editing by Stephen Addison)