The number of investigations into alleged aircraft near misses over Britain has reached its highest level in at least a decade. Official figures show that 213 incidents were reported to aviation chiefs by the end of November last year — almost 25 per cent higher than for the whole of 2013. By the time final data is published for 2014, the number of suspected near misses is likely to be close to the record for a 12-month period, logged a quarter of a century ago. Of those, 18 were the most serious “category A” incidents deemed to pose a risk of collision. Aviation experts said the rise reflected the fact that airspace was becoming scarce as growing numbers of light aircraft, private jets, gliders and unmanned drones take to the skies. About half of incidents involved military aircraft, although the Ministry of Defence denied that there had been any increase in flights in the past 12 months. The disclosure was made after investigators published a report into an incident near Heathrow when a device — believed to be a radio-controlled helicopter — came within 20ft of an incoming passenger plane.