London mayor Sadiq Khan’s trial of scrapping peak-time rail fares on Fridays will begin next week — with a senior figure at Southeastern branding the idea “fantastic” .

Khan announced in January that he wanted to carry out a three-month trial on the Tube and trains beginning this month.  However, the change needed the backing of the National Rail companies that serve the capital to go ahead.

That agreement has been reached, and now nearly all London rail fares, whether on Tube or train, will be charged at off-peak rates from March 8 to May 31. The only exception will be trips to Heathrow airport via zone 1.

The deal includes all stations within the zones, so will take in Swanley and Dartford in Kent as well as SE London’s stations. 60+ London Oyster photocard and Older Persons’ Freedom Passes will also be valid before 9am on Fridays, giving holders free travel.

Some £24 million has been allocated from the City Hall budget, which will be used to compensate TfL and the rail companies for lost revenue and to cover the costs of running the trial. It will be accompanied by a “let’s do Fridays” campaign to encourage people back into central London at the start of the weekend.

Khan said: “Encouraging more people back into the city on Fridays could give a much-needed boost to the hospitality, business and leisure sectors, supporting London’s wider economic growth as we continue to build a fairer, greener and more prosperous London for everyone. So, I’m making a call to all Londoners: to help London keep roaring back – let’s do Fridays!”

Shashi Verma, TfL’s chief technology officer, said: “This trial of making Fridays off-peak will help us better understand how targeted initiatives like this could help potentially support economic growth by encouraging more people back onto public transport and into the office on a day that is currently quieter than other weekdays.”

There had been uncertainty about whether rail companies would take part in the trial, but Thursday night, before the news was confirmed, Southeastern’s director of operations, Scott Brightwell, told Greenwich councillors that the company had been working with TfL on the idea.

“It’s fantastic,” he said. “These are all little levers to try to encourage people to use public transport. We’re well behind that and we’re hopeful that we’ll be able to find a way forward with that.”

He added: “Southeastern are a fan of any promotion that promotes travel on mass transit, whether that be the Underground, or the DLR or mainline rail.”

Initial reporting of Khan’s trial, which, unusually, was released to the media for a Sunday morning, was sketchy with a lack of clarity over whether National Rail companies like Southeastern and Thameslink would participate. The announcement appeared to catch them unawares, when The Greenwich Wire tried to check with the Rail Delivery Group, which represents the operators, it was referred back to TfL.

Scrapping of off-peak fares on Fridays would largely benefit those making simple single or return trips. Peak-time fare caps were abolished inside London in 2015, under Boris Johnson’s mayoralty, in an attempt to help part-time and hybrid workers.