There are just days left to post Christmas cards and packages with Royal Mail, amid fears that backlogs are building as workers launch into six days of strikes.

The postal service has been forced to bring forward its final festive posting dates because of a series of walk outs by employees, which are delaying already bulging mail bags from reaching their destination on time.

Industrial action this month is taking place on December 9, 11, 14, 15, 23 and Christmas Eve as staff - backed by the Communication Workers Union - continue to be locked in an increasingly bitter dispute with bosses over pay and working conditions.

The strikes have prompted Royal Mail to shift final Christmas posting dates - while many businesses report having to turn to to alternative delivery and courier companies in an attempt to guarantee the arrival of goods before December 25.

Electricals retailer Curry's is among those to have announced it has stopped using Royal Mail for smaller shipments in the run up to Christmas - instead temporarily switching to another provider for a small number of parcels in order to ensure they arrive on time.

Customers to have already posted mail with the service are also taking to social media to complain of difficulties using Royal Mail's tracking service, which they claim isn't updating the whereabouts of packages expected to have been dispatched, while other small firms say they are being forced to close online shops earlier than planned so as to avoid disappointment.

Anyone wishing to use Royal Mail has until Monday, December 12 to send items by Second Class post while the deadline for First Class mail is Friday, December 16.

While Royal Mail says it is doing all it can to 'deliver Christmas' and ensure it maintains a level of service during the coming weeks, it is appealing to anyone with a letter or package to send to do so as soon as possible.

A Royal Mail spokesman said: "The CWU is striking at our busiest time, deliberately holding Christmas to ransom for our customers, businesses and families across the country.

"We are doing everything we can to deliver Christmas for our customers and settle this dispute. During the last strike days, we delivered more than 700,000 parcels, and more than 11,000 delivery and processing staff returned to work.

"We recovered our service quickly, but the task becomes more challenging as Christmas nears."