Nicholas Boscawen of Tregothnan near Falmouth in Cornwall was a colonel in Oliver Cromwell's Parliamentary army and was buried in the middle part of the Quire in Westminster Abbey in 1645. He was the eldest son of Hugh Boscawen and his wife Margaret (Rolle) and three of his brothers, Hugh, Charles and Edward, became Members of Parliament. His regiment of horse was mainly composed of his own tenants.
But in 1661, by Royal Warrant dated 9 September, his remains were disinterred, along with other followers of Cromwell, and buried in a pit in St Margaret's churchyard outside the Abbey. In 1966 an inscription was cut in the wall of the tower of St Margaret's recording the names of those who were disinterred:
"This tablet is erected by the Cromwell Association to the memory of the undermentioned whose remains were disinterred from Westminster Abbey at the time of the restoration of King Charles II and were in September 1661 buried in this churchyard of St Margaret's"
It then lists the 21 names including Nicholas. He has no memorial in the Abbey.
Further reading for his father Hugh:
Oxford Dictionary of National Biography 2004.