A new underground train system has been proposed to cut travel times between two cities in the south of England.

The rail link would connect Southampton Central station with Netley, allowing for a more direct and quicker route to neighbouring Portsmouth.

It is one of several ideas suggested in a document released by Transport for the South East (TfSE) that has been put out to public consultation, reports the BBC.

TfSE said its plans would be introduced over a 27-year period.

It said the proposals which, among others, included adding a platform at Portsmouth Harbour and increasing capacity on the Botley line, would cost £45bn in total.

The document said: “A longer term package of interventions is needed to unlock significant capacity and, potentially, shorter journey times between Southampton and Portsmouth city centres.

“This could include developing an entirely new rail link (most likely underground) between Southampton Central and the Netley line.”

Trains between Southampton and Portsmouth typically take between about 40 minutes and an hour.

However, the TfSE said the “transformational capacity and connectivity” of a new line in Southampton would mean services every 15 minutes between the two cities would take 30-35 minutes, said the BBC report.

Councillor Eamonn Keogh, cabinet member for transport and district regeneration at Southampton City Council, said TfSE’s ideas were “ambitious” and would “completely transform the way we travel”.

“Investing in these plans would significantly reduce the air pollution caused by private cars, create thousands of new jobs that would enhance the local economy, and provide much easier and cleaner ways to travel for years to come,” he added.

The consultation on the plans will close on 12 September.