As the yacht headed on a collision course for a treacherous underwater reef, it was not modern technology that saved it from disaster - but a method of warning dating back to the 19th century.

Simon Sugrue was the watch keeper on duty at Bass Point coastwatch station, at The Lizard, when he saw the yacht seemingly unaware it was on course for the Dales - rocks that are submerged at high tide and present a real danger of running aground.

He knew he must take immediate action, but it quickly became apparent that the vessel was not carrying an Automatic Identification System (AIS) beacon.

Unable to contact the yacht’s skipper using the conventional VHF radio, Mr Sugrue took the only other course of action available in the circumstances and flashed the letter U – a Morse code warning for “you are standing into danger” – using the station’s old, but highly effective, Aldis lamp.

Having come within ten boat lengths of the rocks, the yacht was then observed to alter course southwards shortly afterwards and continued safely on its passage to Falmouth.

Mr Sugrue – a former Master Mariner - is no stranger to the Aldis lamp, having started his seagoing career in 1950, when they were still in regular service.

He said: "It was an interesting minute or so on watch, with the Aldis lamp in my right hand and the phone jammed in my ear with an open line to the coastguard, who wanted a running commentary on the unfolding situation."

Peter Clements, station manager at Bass Point, said: "To the best of my knowledge we are one of only a few NCI (National Coastwatch Institution) stations in the country to possess an Aldis lamp.

"The advent of modern technology means that nowadays you are more likely to see an Aldis lamp flashing Morse code messages between ships in a Second World War film about the Atlantic convoys. But in the situation in which our watch keeper found himself, it proved to be the right tool for the job and his quick thinking probably prevented a serious incident."