Hundreds of commuters will be left with standing room only when a new high-speed train service linking Sussex and London comes into service.

Connex South Central has ploughed more than £100 million into the new 100mph trains which will reduce journey times to the capital.

However, they will have 60 fewer seats per carriage than some trains currently in service on the Brighton line.

It means 12 car sets of the new Class 375 trains will have a total of 720 fewer seats than Class 423 slam-door trains which are now widely in use.

The new carriages, to be phased in over the next two years, will however carry more people overall because there is increased space for standing passengers.

Commuters have greeted the news with fury and are demanding an explanation from the firm, which is expecting to hear within weeks if it can continue running services along the line.

Shelley Atlas, of Brighton Line Commuters, said: "They have simply got to have as many seats as they do now because we already have problems with people having to travel for 45 minutes without getting a seat.

"They should be increasing the number of seats for passengers or it is just going to be ridiculous."

Connex has ordered 120 of the Class 375 air-conditioned trains which will replace Mark 1 slam-door models currently in service.

Currently, Class 421 and 423 carriages are mostly used on services from Brighton to London and they have 236 and 302 seats respectively. The firm's express service has 214 seats per carriage.

They will be replaced by the Class 375 carriages, which have 242 seats. It means a four-carriage Class 375 service on the Brighton line will be able to seat 968 passengers compared to 1,208 on a Class 423 train.

Services from Horsham and Uckfield to the capital will get higher density Class 375 trains, with 262 seats.

Connex spokesman David Ewart said: "The trains have more seats than some carriages currently operating on the line, although not others."

The Shadow Strategic Rail Authority is expected to decide next month if Connex can continue running the service. The firm is facing competition from Govia, which runs the Thameslink service.