At approximately the same time as Ney's combined-arms assault on the centre-right of Wellington's line, rallied elements of D'Erlon's I Corps, spearheaded by the 13th Légère, renewed the attack on La Haye Sainte and this time were successful, partly because the King's German Legion's ammunition ran out. However, the Germans had held the centre of the battlefield for almost the entire day, and this had stalled the French advance.

With La Haye Sainte captured, Ney then moved skirmishers and horse artillery up towards Wellington's centre. French artillery began to pulverise the infantry squares at short range with canister. The 30th and 73rd Regiments suffered such heavy losses that they had to combine to form a viable square.

The success Napoleon needed to continue his offensive had occurred. Ney was on the verge of breaking the Anglo-allied centre. Along with this artillery fire a multitude of French tirailleurs occupied the dominant positions behind La Haye Sainte and poured an effective fire into the squares. The situation for the Anglo-allies was now so dire that the 33rd Regiment's colours and all of Halkett's brigade's colours were sent to the rear for safety, described by historian Alessandro Barbero as, "... a measure that was without precedent".

Wellington, noticing the slackening of fire from La Haye Sainte, with his staff rode closer to it. French skirmishers appeared around the building and fired on the British command as it struggled to get away through the hedgerow along the road. Many of Wellington's generals and aides were killed or wounded including FitzRoy Somerset, Canning, de Lancey, Alten and Cooke. The situation was now critical and Wellington, trapped in an infantry square and ignorant of events beyond it, was desperate for the arrival of help from the Prussians.