Royal Mail Group is facing an extra £300m annual bill from its pensions, one year on from a multi-billion-pound deal that was supposed to have solved its pension issues once and for all ahead of a public listing.

The prospect of new pensions difficulties emerged in a letter sent by Royal Mail to its staff and its trade unions this week and seen by Financial News. In the letter it warned them that the pensions issue is not yet solved and they may have to accept curbs on their benefits.