Moderates like Holles grew increasingly desperate to reach agreement with Charles, who refused meaningful concessions, leading Cromwell and his supporters to conclude further talks were pointless. As one of the MPs who backed Holles and voted in favour of continuing negotiations, Rossiter was among those excluded by Pride's Purge on 6 December 1648. Unlike his grandfather, he opposed the Execution of Charles I in January 1649 and spent much of the 1649 to 1660 Interregnum in obscurity. Although elected MP for Lincolnshire in 1654, 1656 and 1659, he was prevented from sitting as a suspected Royalist. This had some merit, as he was allegedly involved in co-ordinating the 1659 Booth's Uprising.