From behind came the call of a trumpet, three blasts ending in a long, higher pitch, again and again. Uxbridge had ordered his heavy cavalry to attack. Two brigades edged forward. There was too little space to launch into a gallop and they could only trot through the gaps in Picton’s division as the infantry hurriedly closed up to let the horsemen by, cheering their mounted comrades on. The horsemen cantered forward, into the massed ranks of the French infantry, hacking and slashing with their heavy blades. For a moment the enemy’s nerve held, but as more British cavalry flowed round their flanks and loomed above them like giants in the thick smoke, their courage left them. The leading ranks turned and pressed into those behind, desperate to escape the swishing sword blades, and the panic communicated itself through the entire formation in moments. Thousands of infantry turned back down the slope and ran, desperately wriggling out of their cumbersome packs as they sought to escape.

‘By God, that was well timed!’ Somerset said as he rose up in his saddle and cupped a hand to his mouth. ‘Ride, men! Ride! Run ’em into the ground!’

Arthur turned to frown at him, about to tell his subordinate to show some restraint, when he caught sight of Uxbridge dashing past, sword drawn and urging his men on at the top of his voice. Then Uxbridge’s’s mount leaped a low stretch of hedge and thundered down the slope in pursuit of the enemy.

On the ridge the battered lines of Picton’s division re-formed their line and Arthur let out a low sigh. The centre had survived the first great test of the battle.

La Belle Alliance, 2.30 p.m.

Napoleon stared in silence at the fleeing mass, borne towards him like confetti. Surging forward through the fleeing figures were the riders of Wellington’s cavalry, closing up on the line of cannon stretching across the middle of the battlefield. The gunners dared not fire for fear of slaughtering their own men and could only watch in dread as the danger swept down the slope towards them. As the first of the British horsemen reached the guns some of the crews tried to defend themselves, using ramrods, handspikes and short swords. It was a brief, unequal struggle and the gunners were quickly driven away from their cannon, hurrying back to find shelter amid the limbers and under caissons. The horsemen pursued them, sabreing any man who came within reach. They also slashed at the tendons of the draught horses to disable them, and the helpless animals collapsed in their traces, whinnying in agony and terror.

Around the Emperor, his staff officers watched the cavalry charge aghast. Only a short time earlier, it had seemed that nothing could stop d’Erlon’s corps from smashing its way through the heart of the allied army. Now all three divisions were scattered and the slope was covered with thousands of bodies.