Yeovil MP David Laws has urged fellow southwest MPs to get together and fight for improved rail services in the region.
Mr Laws made his comments after having received a letter from Richard Bowker, the chairman of the Strategic Rail Authority (SRA).
The Yeovil MP initially approached Mr Bowker in an attempt to improve services in general and initiate the laying of twin tracks where they do not already exist.
Mr Bowker replied saying he agreed there was a need for twin tracks, but also said this would take some time to achieve.
As part of a larger project, the SRA is conducting an investigation to see if the region is better served by a single operator, an exercise for which Mr Bowker disclosed no completion date.
In his reply to Mr Laws he wrote: "More work is needed to define the best solution and how it should be funded.
"I would stress that our commitment is to the whole route, not just Waterloo-Salisbury, and our plans do not envisage a change of train for journeys from Crewkerne or Yeovil Junction to Waterloo."
Mr Laws was pleased that direct services would be maintained but expressed disappointment with the lack of track progress and said: "Single track effectively blocks serious increases in train frequencies, the planning for double tracking should be taking place now.
"The lack of action to improve rail services in the southwest is totally unacceptable, and it is clear that southwest MPs need to come together to fight our corner."