Early in 1643 Lucas raised a regiment of horse, with which he defeated Middleton at Padbury on 1 July. In January 1645 he commanded the forces attacking Nottingham, and soon afterwards, on the recommendation of Prince Rupert, he was made lieutenant-general of the Duke of Newcastle's Northern army. When Newcastle was shut up in York, Lucas and the cavalry remained in the open country, and when Rupert's relieving army crossed the hills into Yorkshire he was quickly joined by Newcastle's squadrons.