The MPs have also been hearing from Cornwall Council, Cornwall Fire and Rescue Service, Falmouth Harbour commissioner Mark Sanson, National Coastwatch Institution and the Royal Yachting association.
South West Trains is operating a limited service of two services per hour and First Great Western is running one service per hour through to Portsmouth Harbour.
Mr Thain might see a merger between Merrill and his old firm or another large bank as his crowning achievement before entering public service (he is believed to harbour political ambitions).
South West Trains (SWT), which is operating a reduced service of two trains an hour to Portsmouth Harbour, said it shared passengers' frustration and was "pressurising Network Rail to complete the work as quickly as it can".