Sealed post boxes have started to be unblocked

Striking Royal Mail staff have begun returning to work on Tuesday, on the advice of their union and the employers.

More than 20,000 workers in London and a dozen regional centres in England were on strike, with letterboxes sealed to prevent the backlog of undelivered letters growing.

Tens of millions of letters have accumulated in the backlog caused by weeks of disruption in some areas.

Staff have already started on the backlog, which Royal Mail says will take weeks to clear.

It probably will take two to three weeks, but we will be working to clear it as soon as we possibly can Barbara Rolston Royal Mail

Barbara Rolston of Royal Mail says the company will be working hard to get its service back to normal for its customers in Northern Ireland.

"Customers can start posting to London again, but they should be aware that items are still likely to suffer delays while we clear the backlog," she said.

"It probably will take two to three weeks, but we will be working to clear it as soon as we possibly can.

"People who have been awaiting mail should begin to see that over the next few days and into the end of the week."

Royal Mail said it would take weeks to deliver the tens of millions of letters, with no special overtime arrangements to help.

The dispute was estimated to be costing the Royal Mail around �10m a day in London alone.