The 1645 campaign began in April when the newly formed New Model Army marched west to relieve Taunton, before being ordered back to lay siege to Oxford, the Royalist wartime capital.

They also lost all their artillery and stores, along with Charles' personal baggage and private papers, which revealed his attempts to bring the Irish Catholic Confederation and foreign mercenaries into the war.

In July 1644, a Parliamentarian force under Sir Thomas Fairfax and Oliver Cromwell secured control of Northern England by victory at Marston Moor.

The two commanders involved, Essex and Manchester, were accused by many in Parliament of lacking commitment, a group that included moderates like Sir William Waller as well as radicals like Cromwell.

As members of the House of Lords, Manchester and Essex were automatically removed since unlike MPs they could not resign their titles, although they could be re-appointed, 'if Parliament approved.

Moderates Fairfax and Philip Skippon were appointed Commander-in-Chief and head of the infantry, respectively; Cromwell remained an MP but was given command of the cavalry on a 'temporary' three-month commission, constantly renewed.

A faction headed by Lord Digby considered the New Model a threat to their capital at Oxford, while a third group preferred to consolidate control of the West Country.

Unlike Prince Rupert who had been beaten by Fairfax and Cromwell the previous summer, Digby and Charles dismissed the fighting capabilities of the New Model.

[10] Although Prince Rupert favoured withdrawing, Digby convinced Charles that retreat would be bad for morale and they decided to stand and fight.

The Royalists occupied a strong position on a ridge between the villages of Little Oxendon and East Farndon about 2 miles (3.2 km) south of Market Harborough.

[13] The Royalist scoutmaster, Sir Francis Ruce, was sent out to find the Parliamentarian army and rode south for 2 or 3 miles (3.2 or 4.8 km) but saw no sign of it, perhaps through negligence.

At the last minute, as the Royalists began to advance, Cromwell sent a regiment of dragoons under Colonel John Okey into the Sulby Hedges, where they could fire into the flank of Rupert's cavalry.

[sic][24] Skippon was wounded by a bullet which splintered his armour and struck him under the ribs, although he stayed on the field to prevent panic from spreading.

Some of Ireton's regiments, on the far left, were saved from destruction by the fire from Okey's dragoons, but the others broke and fled, some of them not stopping until they reached Northampton, 15 miles (24 km) away.

[27] At about the same time, Okey's dragoons mounted their horses and charged from the Sulby Hedges against the right wing of the Royalist infantry, as did some of Ireton's regiments which had partly rallied.

[30] Archaeological evidence, chiefly recovered musket balls, suggests this episode took place in the vicinity of Long Hold Spinney, about 1 kilometre (0.62 mi) behind the original Royalist positions.

[31] At some stage, the King attempted to lead his lifeguard of horse to the rescue of his centre or in a counter-attack against Cromwell's troopers, but was prevented from doing so by a Scottish nobleman, the Earl of Carnwath, who seized his bridle and said, "Would you go upon your death, Sire?"

[31] Many Royalists were slaughtered when they mistakenly followed what they thought was the main road to Leicester into the churchyard in the village of Marston Trussell, and were unable to escape their pursuers.

The Committee of Both Kingdoms responded on 28 June by ordering Leven's Scottish Covenanters to move to strike at the Royalist stronghold of Hereford.

By publishing this correspondence, entitled The King's Cabinet Opened,[37] Parliament gained much support in favour of fighting the war to a finish.