We may all be going on a summer holiday after all. German holiday giant TUI expects a strong 2021 summer season in Europe, saying Wednesday it will operate at 75% of pre-crisis capacity.The global travel slump has hammered the world's biggest holiday group. It reported a $1.6 billion loss for the six months to the end of March. But things are looking up. TUI said that the worst was behind it, and new bookings have doubled since April, with customers from Germany and Belgium driving demand for holidays after winter lockdowns.The group expects UK bookings to catch up as more destinations are opened in the next few weeks.Chief Executive Fritz Joussen said that extending the summer season into October and November was a possibility given the demand.Britain, which is one of TUI's biggest markets, said last week that people could travel again from May 17, but with only a limited list of destinations not requiring quarantine on return.Some of TUI's most popular destinations, such as Spain and Greece, were kept off Britain's "green list" of low-risk destinations, but the company said it expects that to change when the list is reviewed at the end of the month.