The transport secretary today faced accusations of putting “party politics” ahead of improving services to passengers, after a leaked letter emerged in which he expressed desires to keep suburban rail lines “out of the clutches of any future Labour Mayor”.

Mayor of London Sadiq Khan also accused Chris Grayling of breaking a promise, made in January, to “give control of London’s suburban rail lines, like Southern, Southeastern, and South West, to Transport for London (TfL)”.

From January: Transport for London announce takeover of London's suburban rail services

Mr Khan said TfL taking over commuter routes would lead to improved services and that his plans for a takeover had cross-party support, including from council and businesses outside London.

From yesterday: 'Bitterly disappointed': TfL will NOT be taking over Southeastern train services

But Mr Grayling formally rejected the Mayor’s bid to take over commuter routes operated by Southeastern yesterday.

Speaking in parliament, Mr Grayling said that Mr Khan’s proposed rail devolution would be the “biggest operating change on this railway since the 1920s”.

Your Local Guardian:

The Epsom and Ewell MP (pictured above) added: “We can deliver improvements through partnership, but we must remember that that partnership is not just about London.

“It is a partnership that involves passengers on different parts of the routes. We need to design a franchise structure that delivers improvements for everyone.”

Today, a government source close to Mr Grayling reaffirmed his position that handing over control of suburban rail lines to TfL would make operators unaccountable to passengers from outside of London.

The source said: "The mayor's business plan promised a big re-organisation but no extra capacity.

“There are real issues about giving the Mayor control over services to places outside London, when those living there can't vote for him."

In the letter leaked to the Evening Standard, Mr Grayling wrote to then-Mayor, Boris Johnson, about the “possibility of TfL taking on responsibility for a number (of) rail services in the London area, but outside the Greater London boundary”.

It read: “While I am generally a great supporter of what you are doing in London, I would not be in favour of changing the current arrangements – not because I have any fears over the immediate future, but because I would like to keep suburban rail services out of the clutches of any future Labour Mayor.

“The continuation of the system we have at the moment does at least mean that MPs and local authorities from outside the London area would have a remit over train services in our area, which I would not like us to lose.”

Your Local Guardian:

Responding to yesterday’s announcement Mr Khan (pictured above) said: "The only proven way of improving services for passengers is giving control of suburban rail lines to TfL.

“Anything short of this simply won't make the improvements desperately needed.

“It is a fact, TfL lines have more frequent trains, fewer delays and cancellations, more staff at stations and fares are frozen.

“We will keep pushing the government to deliver the rail devolution they have promised and that is needed."

He added: “Commuters across south London and the commuter belt are understandably furious after the government broke their promise to make commuter rail services more frequent, reliable and affordable.

“Instead they are putting forward a much weaker proposal that will have none of those benefits for passengers, businesses and communities more widely.

“This is not about party politics, our plan is supported by MPs and councils from all parties in London, as well as by councils outside of London like Kent, Surrey and Hertfordshire.”

Got a story? Get in touch at craig.richard@london.newsquest.co.uk