He also defended the rights of the commoners of Ely threatened by the "adventurers" who had drained the Great Level, and he was nicknamed afterwards by a royalist newspaper "Lord of the Fens."
In May he defeated a greatly superior royalist force at Grantham, proceeding afterwards to Nottingham in accordance with Essex's plan of penetrating into Yorkshire to relieve the Fairfaxes; where, however, difficulties, arising from jealousies between the officers, and the treachery of John Hotham, whose arrest Cromwell was instrumental in effecting, obliged him to retire again to the association, leaving the Fairfaxes to be defeated at Adwalton Moor.
According to Clarendon the latter, though frequently victorious in a charge, dale, subsequently falling upon and defeating the royalist centre, and pursuing the fugitives as far as the outskirts of Leicester.
Cromwell was present at the sieges of Bridgwater, Bath, Sherborne and Bristol; and later, in command of four regiments of foot and three of horse, he was employed in clearing Wiltshire and Hampshire of the royalist garrisons.
These votes, however, were cancelled later, on the 26th of July, under the pressure of the royalist city mob which invaded the two Houses; but the two speakers, with eight peers and fifty-seven members of the Commons, themselves joined the army, which now advanced to London, overawing all resistance, escorting the fugitive members in triumph to Westminster on the 6th of August, and obliging the parliament on the 10th to cancel the last votes, with the threat of a regiment of cavalry drawn up by Cromwell in Hyde Park.