On 24 Dec. 1642 Rosworme took part in a sally to prevent Lord Derby making head and again attacking Manchester. They broke the royalist force at Chowbent and captured Leigh, returning within three days. Manchester was thus secured to the parliament, and confidence was given to the parliamentary cause throughout Lancashire and the adjoining counties. On 2 Jan. 1643 Lord Wharton appointed Rosworme lieutenant-colonel of Ashton's regiment of foot, and in February he joined the regiments of Sir John Seaton and Colonel Holland in an attack on Preston. It was captured by assault on the 9th, and Rosworme remained to fortify the place.
On the termination of his half-year's engagement with Manchester, Rosworme was induced to execute a new contract by which in return for a yearly salary of 60l., to be paid quarterly, during the life of himself and his wife, he bound himself to finish the fortifications of Manchester and to carry out all military affairs for the safety of the town on all occasions. He further agreed to forego his position as lieutenant-colonel in Ashton's regiment, and to accept instead the command of a foot company of the garrison of Manchester.
On 1 April 1643, having finished the fortifications of Manchester, Rosworme, although it was outside his contract, accompanied a force to attack Wigan. A gallant assault, chiefly by Ashton's regiment, took the town in less than an hour; but the enemy held the church, which surrendered after a desperate struggle. While Rosworme was receiving the garrison's arms and making preparations for their convoy, he found that Colonel Holland, the parliamentary commander, had marched away, leaving only one company to convoy four hundred prisoners, arms, and ordnance through a hostile town. There was nothing left for him but to escape as quickly as possible to Manchester. Holland's conduct was investigated by a committee in London on 15 April, and Rosworme and others attended to give evidence. Holland's influence and his many friends in parliament saved him from punishment. Thenceforth, however, he became Rosworme's enemy, and succeeding in stopping his pay as a captain for a year, on the pretext that Rosworme had not taken the covenant.
Rosworme took part in the unsuccessful attack on Warrington on 5 April 1643. In May he fortified Liverpool. On 5 July the Earl of Newcastle, having defeated the parliamentarians at Wisked Hill, Adwalton Moor, Yorkshire, and having taken Bradford, summoned Manchester. The town sent Rosworme to reconnoitre and strengthen the positions of Blackstone Edge and Blackgate, by which Lord Newcastle must approach Manchester. Considerable works of defence were erected, two pieces of ordnance mounted, and strong garrisons posted. Newcastle, hearing that the positions were impregnable, relinquished the project, and went to the siege of Hull. In January 1644 Rosworme accompanied Sir Thomas Fairfax to raise the siege of Nantwich, and was present at the battle of the 25th, returning later to Manchester. In August he accompanied Sir John Meldrum [q. v.] to the siege of Liverpool; the town had been captured by Prince Rupert the month before. Rosworme was master of the ordnance and director of the siege, which lasted ten weeks; the town capitulated on 1 Nov. In 1645 the royalists again attempted to bribe Rosworme into surrendering Manchester, and thus divert the parliamentary forces from the siege of York. Having learned all the details of the royalists' design, Rosworme disclosed it to the chief men of the town, who made ‘deep protestations and promises’ to give him pensions amounting in all to 100l., according to their means, when peace should come. Rosworme put the town in such an efficient state of defence, and showed so bold a front, that the royalists left it alone. He was now in great favour, and the town sent an importunate petition to the House of Commons for the payment of the arrears due to him, and of ‘a handsome gratuity for his desert.’ An order of council dated 4 Sept. directed the payment of the arrears, but admonished the Manchester people for the non-payment of the stipulated pension!
During the plague which broke out in the summer Rosworme refused to quit Manchester, and with a dozen of his men rendered invaluable assistance to the sick, and maintained order among the inhabitants. He received scant reward. His pension was unpaid and his pay allowed again to fall into arrear because he refused to sign the covenant. In 1648 his reduced circumstances compelled him to visit London to endeavour to obtain redress. There he published a pamphlet, dated 9 May, containing a violent attack upon the twenty-two men who signed the agreement with him on behalf of the town of Manchester. The Scots were advancing south. The town, anticipating danger, therefore recalled Rosworme, and paid him the arrears of his military pay, but not his pension. Towards the end of the year the town was again in his debt, and he went to London to petition the House of Commons. He also wrote a bitterly worded
