He resumed his seat in the House of Lords, while an attempt to impeach him for treason was blocked by Denzil Holles, head of the "Peace" faction in Parliament. Rich was one of ten lords appointed to the Westminster Assembly, a body established with Scottish representatives to agree reforms for the Church of England. By the time Charles surrendered in June 1646, his opponents were divided between moderates led by Holles who dominated Parliament and radicals within the New Model Army, headed by Oliver Cromwell. After negotiations between the king and Parliament broke down in late 1647, the Scots, English moderates and Royalists created an alliance to restore Charles to the throne. The Second English Civil War began in April 1648.