Staff began to return to work on Monday

All staff returned to work on Tuesday after a basic "get back to work" deal was struck following almost two weeks of wildcat action.

The company and unions began meeting at Acas to iron out more substantive remaining issues.

These are understood to involve moving to a single post delivery, and more flexible working arrangements.

Royal Mail says the build-up of post could take at least a fortnight to clear.

Special Delivery services fully resumed on Tuesday after being suspended in some areas, while post boxes in London which had been sealed were unblocked.

On Monday, Downing Street issued a statement welcoming the deal under which staff returned to work, but warning that more needed to be done.

HOW BAD IS THE DISRUPTION NOW? Royal Mail say a full complement of staff have returned to work Post, especially in London, likely to remain disrupted for two to three weeks because of a backlog of millions of items Sealed post boxes in London being unsealed from Monday Special Delivery services, suspended in some areas, now resumed. Items in backlog treated as priority Guide to the affected areas

"This does mark progress but there are still things that need to be worked through and we obviously hope they will be," it said.

"It's important for customers, employers and employees that this is resolved as soon as possible."

Trade and Industry Secretary Patricia Hewitt defended the government for not getting more involved.

"It is not for the government to try to micro-manage the Royal Mail or get involved in the negotiations," she told BBC Radio 4's PM show.

"I have made it very clear that I expect the management and the union to work together and to create an effective partnership in the Royal Mail in place of the frankly appalling relations that existed up until a couple of years ago.

"I am very pleased that [the two sides have] reached an agreement on this to stop these unofficial strikes and get the company back to work."

More than 20,000 workers in London and about a dozen regional centres were on strike at the peak of the action.

Communication Workers' Union deputy general secretary Dave Ward said the causes of the dispute involved many offices and many local working practices.