The alarm was raised when a woman reported her husband was among five adults and four children travelling through the Strait of Dover on two rigid-hulled inflatable boats (RHIB).

She told Dover Coastguard her husband telephoned her to say his vessel had lost the second RHIB after they set off together from Boulogne destined for Dover, a journey of more than 25 miles.

A large-scale air-sea search was launched just after 6pm with the Langdon Coastguard rescue team, the Dover RNLI lifeboat and the Coastguard spotter plane based at Manston airport.

The Coastguard tug Anglian Monarch and the Dover Harbour board police were also drafted in to help.

The Maritime and Coastguard Agency (MCA) said a motor tanker in the Strait reported that they had seen the missing craft.

The Coastguard spotter plane flew to the position was able to direct the lifeboat crew to them as winds gusted to gale force eight.

A Dover Coastguard spokesman said the sailors were unhurt but "extremely foolhardy" to set off with inadequate clothing and without properly using their communications system.