LONDON (Reuters) – London’s Heathrow Airport said on Monday that May was its busiest month since March 2020 as it dealt with 5.3 million passengers, 79% of 2019 levels. Cancelled flights, long queues and staff shortages at UK airports disrupted the travel plans of British holidaymakers during the Jubilee half-term break. However, Heathrow said its check-in generally worked well in May, with more passengers checking-in online, while 90% of passengers went through security in less than ten minutes. It said no more flights were cancelled at short notice than on any normal day and Border Force per…