Royal Mail will take longer to deliver millions of business letters as part of a trial ahead of official changes to regulations.

The Ofcom watchdog will consult on an overhaul of postal services next year, including plans to cut second-class deliveries to every other working day. 

But Royal Mail is preparing to introduce changes for bulk letters, such as bills, bank statements and some NHS letters, ahead of that.

It comes at a critical time for Royal Mail's owner International Distribution Services, which is being bought by Czech billionaire Daniel Kretinsky.

The sale is being investigated under national security legislation.

Royal Mail must deliver letters six days a week to 32million homes for the fixed price of a stamp, under the Universal Service Obligation. 

The postal service has been lobbying for a change for four years, saying the commitment costs it £2million a day. 

Under rules being looked at by Ofcom, homes would receive second-class post on Monday, Wednesday and Friday one week, then Tuesday and Thursday the next, with the letters arriving within three working days.

However, Royal Mail is planning to launch the changes for bulk business letters before Ofcom's ruling to give customers more time to prepare.

The current service, which sees second-class letters delivered within two days and includes Saturdays, will be phased out if Ofcom gives the go-ahead in early 2025 for the changes to go ahead later that year.