The trains, which originate in Eastbourne, are only four carriages long, meaning that people are left standing the entire journey of around an hour and a half, if they are able to get on at all, said the MP.
Putting four-carriage trains on during peak hours on a commuter route is outrageous, and must be stopped,” she said.
“It is simply not good enough that people are paying around £4,500 for a season ticket and then either cannot get on the train or are standing for whole journeys.
“I will make sure that the issue is kept on the minds of both Government and Southern Rail.”
Speaking during a session of Business of the House of Commons questions, she said: “May we have a statement on the issue of short formation trains?
“In Lewes, on peak services, we still get four-carriage trains, and passengers who pay an average of £4,500 a year for a season ticket cannot get on them.
“Will the Leader of the House ask for a statement from the Department for Transport?”
The minister agreed that he would forward the request to ministers at the Department for Transport.
However there are more pressing things in Parliament at the moment so it looks like the hard done commuter will still continue to suffer.