Whilst Brentford had been a tactical victory for the royalists, the campaign had not been a strategic success.  Its ultimate objective had always been the capture of London; implicitly, once the parliamentarian field army had been eliminated.   But Essex’s army had not been destroyed at Edgehill and the royalist high command, Prince Rupert notwithstanding, were cautious about a rapid advance on the capital.  Instead a race with Essex was rejected and a strategy which allowed consolidation of gains on the march to London adopted.  But the ease of the royalist advance on London and no doubt Rupert’s encouragement, appears to have persuaded the King to press his advantage with the attack on Brentford and subsequent confrontation at Turnham Green.    

But the attack and sack of Brentford, when in the midst of peace negotiations,  hardened parliamentarian sentiment against accommodation and rallied opinion in parliament and the City in favour of a stand against the King.  The King appears to have realised the impact of his actions belatedly.  As his army retreated from London toward Oxford later in November, he wrote to parliament claiming that the battle at Brentford had resulted because both armies were in such close proximity, that he had been unable to prevent the clash and that he was still willing to continue negotiations.   However, he also justified the attack on the grounds that to have let parliament’s forces garrison Brentford would have left the Royal army surrounded, with parliamentary troops in the Colnbrook area and at Windsor, Kingston, Uxbridge and Acton.  But by marching on Brentford, Charles had placed his army at greater risk of encirclement than if he had remained farther to the west of London. 

After Turnham Green there were recriminations in some royalist quarters that the King had lost an opportunity to win the war.  But the extent of enclosure around the Turnham Green and the fact that the royalists were outnumbered two to one by the defending parliamentarian forces made this proposition highly unlikely.  The King’s best chance had in reality been the day before at Brentford. Had the royal army not been held-up by the parliamentary delaying action there, more progress could have been made against London.  The parliamentary field army was dispersed, the trained bands were not mustered together and the parliamentary artillery train at Hammersmith might well have been captured.   Nonetheless the extent of enclosure on the western side of London, the defensive works built rapidly to protect the capital after Edgehill and the threat from parliamentary forces in the royalists’ rear would still have made such an advance risky and the outcome unpredictable.