While Waller continued to shadow the King, Essex marched into the West Country, to relieve Lyme which was under siege, and then to subdue Devon and Cornwall.

Waller's army, most of which was unwilling to serve far from its home areas in London and the southeast,[2] was subsequently crippled for several weeks by desertions and threatened mutinies.

Although Essex himself escaped in a fishing boat and his cavalry broke out of encirclement, the rest of his army was forced to surrender on 2 September, losing their arms and equipment.

[3][4] After the victory at Lostwithiel, King Charles first probed the Parliamentarian defences at Plymouth[5] then marched back across the southern counties of England to relieve several garrisons (including Banbury, Basing House and Donnington Castle, near Newbury), which had been isolated while he had been campaigning in the west.

[6] King Charles was joined briefly by Prince Rupert, who had been defeated at the Battle of Marston Moor in northern England on 2 July.

The Earl of Essex also arrived at Basingstoke on 20 October with an army composed largely of elements of the cavalry and infantry that had survived the battle at Lostwithiel.

Charles' army held three strong points: Donnington Castle north of Newbury, Shaw House northeast of the town and the village of Speen to the west.

Early on 26 October, the combined Parliamentarian armies advanced to Clay Hill, a few miles east of Newbury, where they set up an artillery battery.

His force broke camp and resumed its outflanking move on 27 October while Manchester launched a diversionary attack on Shaw House.

Although the Royalists at Donnington Castle observed Waller's movement, and even sent a small detachment of cavalry to harry his rearguard, the troops at Speen were not warned of the danger.

[11] Balfour routed Maurice's cavalry and also defeated the Earl of Cleveland's brigade, but was then checked by the fresh Queen's Regiment of horse and musketeers under Sir Thomas Blagge lining hedges east of Speen.

The Earl of Manchester was slow to throw in his own attack, pleading that the noise of Waller's guns had not been heard over the exchanges of artillery fire at Shaw House.

Cromwell, Balfour and Sir Arthur Hesilrige eventually were allowed to take cavalry in pursuit of the King's army, but soon found that the Royalists had already crossed the River Thames at Wallingford and had reached the safety of the neighbourhood of Oxford.

[15] The dissatisfaction expressed by Cromwell and other Parliamentarians over the failure to trap Charles after the battle and the subsequent half-hearted operations, eventually resulted in the passing of the Self-denying Ordinance, which deprived Essex, Waller and Manchester of their commands, and the formation of the New Model Army, with which Parliament gained victory the next year.