What Sheffield really says,

"One undeniable fact is that Britain and its allies, not Germany, won the First World War. Moreover, Haig's army played the leading role in defeating the German forces in the crucial battles of 1918. In terms of the numbers of German divisions engaged, the numbers of prisoners and guns captured, the importance of the stakes and the toughness of the enemy, the 1918 'Hundred Days' campaign rates as the greatest series of victories in British history.

Even the Somme (1916) and Passchendaele (1917), battles that have become by-words for murderous futility, not only had sensible strategic rationales but qualified as British strategic successes, not least in the amount of attritional damage they inflicted on the Germans."

"He(Haig) encouraged the development of advanced weaponry such as tanks, machine guns and aircraft. He, like Rawlinson and a host of other commanders at all levels in the BEF, learned from experience. The result was that by 1918 the British army was second to none in its modernity and military ability. It was led by men who, if not military geniuses, were at least thoroughly competent commanders. The victory in 1918 was the payoff. The 'lions led by donkeys' tag should be dismissed for what it is - a misleading caricature."
http://www.bbc.co.uk/history/worldwars/wwone/lions_donkeys_01.shtml