RPSAG - launched last October after Railtrack was put into administration by transport secretary Stephen Byers - has initially tasked Grandfield with boosting its membership and support.
The group has already signed-up 20,000 paying members, but Grandfield will now target via a media and mailshot campaign the remaining 180,000 private investors who bought Railtrack shares.
Further lobbying and media relations work will centre on getting what it considersfair value from the Government, which is proposing an offer of around £2.50 a share.
'There's up to two months of time in which the Government could be influenced and pressure could be brought to bear before the EGM,' said Grandfield chairman Charles Cook.
'We will be making it plain that the private investors are in no way fat cats - they are people who have been encouraged to invest in Railtrack only to have the rug pulled from under their feet,' added Cook.