Brussels. A spokesman for Eurostar advised passengers to allow a little extra time to clear immigration because of anticipated "slightly longer" queuing times. With the contingency plans still unclear Eurotunnel voiced fears that motorists using the shuttle train across the Channel could face delays with traffic backing up onto the French motorway network. "We still don't know how many staff will go on strike," said a Eurotunnel spokesman. "Although traffic volumes will be low, it doesn't take long for queues to build up and frustration grows very quickly." Back in Britain, Gatwick airport is drawing up its own contingency plans to handle the 28,000 arrivals due on Wednesday. It is setting aside holding areas within terminals to accommodate passengers, rather than leaving them on aircraft until the immigration hall can deal with them. Meanwhile Heathrow said it had received an encouraging response from airlines to its appeal to fly planes half empty to ease pressure on the airport. Several airlines, including Virgin Atlantic, British Airways and bmi have said that passengers can reschedule their flights if they wish to avoid arriving during the strike. However Heathrow has the option of cancelling flights if necessary to keep the airport moving and prevent the chaos extending throughout the week.