Britain’s Olympic security plans fell under fresh scrutiny, with a newspaper reporting that several people on a terror watch list have been waved through airport border controls without being flagged and officials trying to calm the uproar over a security contractor’s failure to provide its promised number of staff.

The Observer newspaper’s report is the latest in a series of lastminute concerns to surface as London gets ready to host the Olympic Games from July 27 to August 12.

The paper said that, since the start of the month, immigration staff at London’s Heathrow Airport had missed several people on a security watch list whose arrival in the country was meant to have been reported to counter-terrorism police or Britain’s domestic intelligence service.

The newspaper cited unions as suggesting that staff brought in to help relieve the pressure at Heathrow, which has faced recurring problems handling large influxes of passengers, weren’t being properly trained. The airport, Europe’s busiest, has recently struggled to clear huge lines that build up at immigration checkpoints during peak times, leading to fears of Olympics-related chaos as tourists fly in to watch the games.