British police on Sunday questioned 22 suspects in an alleged plot to bomb trans-Atlantic jetliners in mid-air, as the country's top law-and-order official warned the risk of another attack remained high. Home Secretary John Reid said the threat "is a chronic one and it is a severe one." Reid repeated the assertion, made before by police, that Britain has foiled four major terrorist plots since the July 7, 2005 London transit bombings, and said police were conducting about 24 anti-terrorist investigations. Britain's terrorist threat level remained "critical" - its highest designation - and delays, flight cancellations and intense security continued to greet many travelers at London airports. "We believe we have the main targets from this particular surveillance and plot," Reid told British Broadcasting Corp. television. "(But) there are still people out there who would carry out such attacks."