Design work on the Metropolitan Line Extension is continuing, according to a stakeholder in the development.

In emails seen by the Observer, Ben Thomas, the TfL stakeholder communications manager, confirms that work is ongoing.

In the emails, dated April 24, Mr Thomas says: “I can confirm that design works are continuing as planned with the agreement of our funding partners, and good progress is being made with this and we are on track to complete those designs by the summer, as planned.

READ MORE: Met Line extension: Mayor to use 'charm offensive' to save multi-million pound scheme

“I understand that funding partners are in ongoing discussions, but I’m afraid that at this stage there’s nothing to report about any movement on the wider funding issues.

“Since taking on the MLX from Hertfordshire County Council in 2015, TfL has been undertaking a detailed review to establish firmer costs of the project.

"Following this extensive work, we estimate that to complete the extension we would need to double the funding commitment we have already made, requiring more than an additional £50m that TfL are simply unable to provide.”

READ MORE: Met Line Extension: £130m of taxpayers' money spent on project

He goes on to explain that the Mayor Of London, Sadiq Khan, believes furthers discussions are needed with the Department for Transport and other funding partners about how the extension's “cost pressures” will be met.

He also said design work should be completed by late July.