Royal Mail will deliver second class post every other weekday and scrap the service on Saturdays as part of a £500m plan to address late deliveries.
The postal company said no changes will be made to first class post and parcels will continue to be delivered up to seven days a week.
Its quality of service improvement plan sets out how Royal Mail intends to achieve a higher standard of service and focuses on addressing completion rates of delivery routes each day, which it said was the primary driver of delays.
The company said the changes were the most significant that it had made for a generation.
It follows heavy criticism of the postal service and a finding by Citizens Advice that Royal Mail failed to deliver post on time to around 16 million people over Christmas.
Boss Daniel Křetínský was hauled before MPs last month to answer questions about the service it was providing.
Alistair Cochrane, CEO at Royal Mail, said: “I’m pleased we’ve reached agreement with our unions – the CWU and Unite CMA - on the rollout of a new universal service delivery model which will deliver a better, more reliable service for our customers, our people and the nation.
“We recognise our service hasn’t always been the standard our customers rightly expect and we’re determined to do better.
“The plan we’ve set out today shows how we’ll make a step change in performance across the UK, backed by £500 million of investment over the next five years.”
