The reasons why England has so many ancient oaks are all historical. It has nothing to do with the climate, the soil, or the geographical distribution of the two species of native oak. The climate is suitable in most of mainland Europe and only becomes unsuitable in the far north and around the Mediterranean Sea. Oaks do not grow better or faster in England than elsewhere, and they are just as common in other parts of Europe. The range of soil types oaks can do well on is great, from light sand to heavy clay and from neutral to acidic, and these too are present in much of Europe. The two oaks are common from Spain to the Caucasus and from Sweden to Italy. Human interference in the forest was similar across Europe from prehistoric time and often favoured oaks.
Things began to differ in the Middle Ages, in particular after the conquest of England by the Normans in 1066. William I considered the entire country his property, gained by conquest. He gave it out in use to his vassals, mostly fellow Normans, and to the Church. Royal Forests were created in which the king had exclusive rights of the 'venison and vert' or the deer and the trees. Privileged hunting, not forestry was the purpose, no kings of the Middle Ages wanted to plant trees in the forests. At its heyday a century after the conquest, perhaps ¼ of England fell under Forest Law, separate from Common Law. It was a form of protection of trees not equalled at this scale elsewhere in Europe.
Of course it did not last. Bit by bit the forests were nibbled away, mainly by 'assarts' or enclaves of agriculture. People lived in the forests; there was population growth of perhaps 300% until the crash of the Black Death in 1348-50. But the forests were also given away to the nobles, the Church and to abbots of monasteries. Many of them created deer parks. The Normans introduced fallow deer from southern Europe, better suited for the parks than the native red or roe deer. It became an English craze. These parks provided even more effective protection of native trees than the forests, because it was easier to exclude the people from a deer park than from a forest. Evidence for this comes from the fact that pollard oaks (used by the people) are less common in ancient deer parks than in forests, chases and commons.
Private landownership and its more or less conservative management prevailed in England on a much larger scale than on the continent. Revolutions and devastating wars have swept away private parks and hunting forests in much of Europe, while the only serious damage done in the past in England occurred during the Civil War (1642-51) and was mostly repaired soon after. Modern destruction of ancient trees from economic activity did not spare England, but one of these, plantation forestry, developed in England on a large scale only after World War I, on the continent at least two centuries earlier. Here, there was less time to convert all the ancient wooded parkland and forest remnants to conifers, and many landowners preferred to continue shooting pheasants and the occasional deer and to use the park in accordance with the fashionable notions of nature of the Romantic period. Britons could obtain their timber through imports from overseas, until the German U-boats of WWI made them think again. Between 1919 (the start of the Forestry Commission) and an urge to "plant, plant, plant!" and the first efforts to halt the destruction in the 1980s there were only 60 years and another World War which further delayed things. These historical developments are mainly responsible for the abundance of ancient oaks in England.