Sir Arthur Bonsall.

Bletchley Park codebreaker.

Born: June 25, 1917

Died: November 26. 2014.

Sir Arthur Bonsall, always known as Bill, who has died aged 97, was one of the last of the Second World War Bletchley Park codebreakers, he and his small staff specifically intercepting the plans of the Nazi Luftwaffe to "soften up" Britain for Hitler's planned land invasion.

Arthur Bonsall was also arguably the inventor of the so-called spy plane, in his day piloted planes whose role was not to bomb but to listen to enemy air-defence communications. It was a breakthrough which must have saved countless of thousands of lives during the Battle of Britain, giving the RAF and ground staff advance knowledge of Luftwaffe targets. The Blitz of London, Glasgow, Coventry and other UK cities may well have been worse but for the work of Arthur Bonsall and his team.

Nowadays, spy planes are vital to warfare, not least through pilotless drones. Sir Arthur Bonsall's wartime work was in defence of the UK and the free world. He could have had no idea then that spy planes, including pilotless drones, would later have a licence to kill, controlled by someone on the other side of the world using a computer and play-station-like controls. He probably would not have liked that.

Neither did he express joy over the fact that his aerial surveillance techniques allowed the RAF to kill hundreds of thousands of German civilians during the war, with the excuse, not his, that "they bombed our cities. We'll bomb theirs." He was also the first to admit that spy planes could not stop, indeed might even exacerbate committed, fanatical or deranged people on the ground who looked to their "God" to absolve them of their barbarity.

Sir Arthur went on after the war to head Bletchley Park's post-war legacy, which became known as the Government Communications Headquarters (GCHQ), now nicknamed "the doughnut" outside Cheltenham, once a top secret facility modelled on the CIA's Langley, Virginia, headquarters, now more of a tourist attraction, not least to supporters of the whistleblower Edward Snowden.

GCHQ had long been accused of possibly listening to all of our phone calls, including the so-called Squidgy Tapes allegedly from Prince Charles to his then friend Camilla Parker-Bowles. Snowden alleged that GCHQ was monitoring all of us, some more than others, but most notably the phone conversations, e-mail and computer records of politicians.

Sir Arthur Bonsall, by chance, became a father of the GCHQ. But he did not like what it went on to do. His drive during the war was to save British lives, not spy on them. When GCHQ became something of a satellite of US intelligence, for better or worse, he did what he was trained to do. He kept quiet.

Arthur Wilfred Bonsall was born in Middlesbrough on June 25 1917 but he was brought up in North London and later in Welwyn Garden City, Hertfordshire. He went to Bishop's Stortford College before going to university at Cambridge (St Catharine's College) to study languages. Like all students at Oxbridge before and after, they were watched by university staff to check their "suitability" for service to the nation. It was at Cambridge University that a "buller" -- a private campus policeman given a few bob a week by a man he promised never to recognise -- first spotted young Bonsall's potential credentials.

Indeed, Bonsall had the spots and the specs. He was clearly brilliant but looked geeky and harmless and the university doctor said he had a heart murmur which made him vulnerable and manipulative. For GCHQ, and British intelligence, he was the perfect candidate. By all accounts, that has not changed. "This chap approached me and said 'are you interested in any confidential war work.' I was a student. Who would have said no?" Bosnall recalled.

According to one journalist, although he was too young to be present at the time, Sir Arthur spoke of his time at Bletchley Park with the emphasis on security and secrecy. "Do not talk at the lunch table. Do not talk in cars or buses. Do not talk in the billet. Do not talk by your own fireside." Sir Arthur never did.

At GCHQ, and eventually as its director from 1973-78, Sir Arthur (he was knighted in 1977) dealt with Cold War issues potentially as explosive, even more so, than the Second World War. In the 1950s and into the 60s, he was a key, though low-key British figure in global politics, with vital input, in the Suez crisis, the Soviet invasion of Hungary and Fidel Castro's takeover of Cuba. The stand-off between Castro and US President John F Kennedy, over Soviet missiles in Cuba, was probably the most memorable but frightening moment of his career.

Sir Arthur Bonsall was married to Joan Wingfield, who died in 1990. They had four sons and three daughters. He died in Cheltenham.

PHIL DAVISON