Bigger Britain

Take the British Isles. Double their size and move them southwest, until the River Thames feeds out into the Bay of Biscay, and the Shetland Islands sit on top of where Scotland rests today. Our POD is the assumption that this vast change came about somehow through nature. Perhaps, during the breakup of Laurasia, the rock formations that would later become OTL Britain were subtly shifted, and eventually grew to become the islands shown here. No matter; what would the effect of a Bigger Britain be on Europe, and the world?

''Author note: this is a sketch of an althist, not a fully-envisaged one. It's most likely that history would not have proceeded down this route even if the POD occurred at all. I'm trying to keep history roughly in line with hours, for the sake of simplicitly, rather than exploring every butterfly.''

Various changes

 * Due to the amount of available land, and closer relations to the Gallic tribes, British tribes are slightly more centralised in organisation than their OTL counterparts.
 * Pytheas' expedition to Britain was not viewed on with as much scepticism as OTL. Greek settlers were already dimly aware of the island through hearsay that had reached colonies in Massillia. Furthermore. Pytheas decided to explore Britain more closely rather than sail to 'Thule', and from that experience make claims that his fellow Greeks found hard to believe (confusing pack ice for jellyfish, and not seeing the midnight sun). He was subsequently better remembered throughout history and inspired several more expeditions to Britain, though no attempts at colonisation were made.
 * The information gathered allows Julius Caesar to make a more calculated invasion of Britain during his conquests. His initial venture in 55BC causes him to ally with the Iceni clan in Norfolk; when he returns in 54 BC, he conquers all of OTL East Anglia, Kent, and Surrey, then departs via the 36-mile crossing to Iberia.
 * The conquest of English and Welsh territory begins roughly the same time as OTL, and proceeds to similar success. However, as the Iceni were one of the first peoples subjugated, Bodicea never becomes the threat she was in OTL, and subsequently there is no revolt. Colchester remains the capital of Roman Britain, due to its strategic position located at the midpoint between the Norfolk-Brest and Kent-Lugo crossings, as well as commanding position over the Gulf of Biscay, a Roman lake.