Proposals to build another train line From London to Brighton must not derail planned improvements in the East Croydon area.

This is the message from Croydon Central MP Gavin Barwell after the Chancellor George Osborne announced he is committing £100,000 to a study to investigate the viability of Brighton Mainline 2 (BML2) earlier this month.

Campaigners supporting the BML2 say the London phase of the project would reopen Selsdon to Elmers End to rail travel to avoid the East Croydon bottleneck and provide a direct link from Kent and Sussex to Canary Wharf and East London.

They also say a Croydon Gateway station would be created - possibly amalgamating Purley Oaks, Sanderstead and South Croydon - providing an interchange between the current line and BML2.

Campaigners also say it would link into Thameslink 2 between Stratford and Lewisham, providing a rail link between Gatwick and Stansted airports.

But Mr Barwell said if BML2 is built it would join the existing line just south of East Croydon so would not improve congestion on the line to the north of East Croydon station.

It would also affect the tram network as it is proposed to use the tunnel that goes from Coombe Road to Sandilands.

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The proposed route for the new line

Mr Barwell said: "The priority should be to improve the existing Brighton Main Line and not Brighton Main Line 2 which I don’t believe would alleviate the core issues facing Croydon commuters.

"Firstly, the proposed new line would join the existing line just to the south of East Croydon.

"But all of the existing problems, including heavy congestion on the routes into London, are caused to the north of the station.

"Secondly, Brighton Main Line 2 uses part of what is a disused railway.

"Part of that forms the basis for the Croydon Tram Network and so significant disruption would be caused should these works commence."

A website promoting the plan admits that the route would compromise the existing Tramlink.

The site states: "About a mile of Tramlink’s New Addington branch occupies the former heavy rail tunnels and will need realigning between Lloyd Park and Lebanon Road. That will be costly, but well worth the stupendous benefit it releases in rail capacity. Further north, the section to Elmers End could easily share the rail corridor, running alongside as the boundary is sufficiently wide."

A Department for Transport spokesman said: "We know the importance of good rail links, which is why we are investing record amounts in building a world-class rail network as part of our long term economic plan.

"We continue to look at the options for improving capacity between Brighton and London, and further updates will be provided in due course."