LONDON (Reuters) -Long traffic jams built up on Saturday outside the Port of Dover, Britain’s main gateway to Europe, and officials said the disruption could be worse than the logjam seen on Friday. Travellers setting out at the start of the British school summer holidays, as well as the usual flow of goods lorries, have faced long delays because of slow border checks. The Kent Resilience Forum, which brings together local councils and emergency services, declared a “major incident”, while Port of Dover CEO Doug Bannister said travellers could face delays of up to six hours on Saturday. The UK…