So this is what I gave them. I got nothing back from them except a free pass for life, so I imagine it went down like a lead balloon.

There are heaps of veterans to Bletchley Park in the book you sent me, so I shall enjoy doing back 60 years in – bloody hell – is it really so long ago? Like you, I only feel 17.

I reported at the entrance, was escorted by an armed military policeman several flights underground, entered a room bare of all save a desk, two chairs and a stern hatchet-faced gentleman in civilian clothes who proceeded to question me about my interest. Was mathematics a subject which naturally appealed to me? No. Did I enjoy chess? No. What about crosswords – did I for instance tackle the Times? No.

I knew that I was not impressing, and being of the age when not to impress anybody at all, about anything at all, was a matter of major concern, I offered "I do translate the fourth leader into Latin twice a week."

Eyebrows were raised and I sensed that the invitation to terminate the interview, which was just about to be given, was being put on hold.

With whom, I was asked, did I translate the Times fourth leader into Latin?

"With Cyril Allington, former Provost of Eton, now Dean of Durham. He makes me take snuff before we begin in order to clear my head."

The raised eyebrows were joined by the bottom half of a smile. A short silence.

"Right. I am going to give you a test. You need this sheet of paper and this pencil to answer. You are standing twenty yards away from a circular brick wall fifteen feet high and with a diameter of forty paces. There is a single entrance gate on the right of the wall. Inside, the grass is a foot high. From where you are standing now a cricket ball has been thrown into the garden Please draw for me the track which you would follow from the gate in order to find the ball."

I spoke aloud as I drew. "I would divide the circle into two hemispheres by walking from the gate across the diameter line from three o'clock to nine o'clock. I would ignore the left-hand hemisphere for the moment since the arc of the falling ball would make it more probably that the location was further from the thrower, i.e. in the right hemisphere. Next I would make an about-right-turn and walk back parallel to, and one foot away from my first track until I again came to the wall and so on in diminishing lengths until I arrived at the top of the circular i.e. at twelve o'clock. I would then mirror the exercise in the other hemisphere."

Bulls eye. Suddenly I was "My dear chap!! You are exactly what we are looking for! We don't want people who think in circles – ninety per cent of the people we see here wander round and round looking for their own backsides – we want those who think in straight lines. You'll do. We'll be in touch." And I left not knowing whether I was to be rowed ashore from a submarine at St. Malo, shuffled by plane to a cornfield near Amiens or locked up in a cubby-hole with a tin of snuff.

POSTSCRIPT . I was astonished to see on television recently that the GCHQ building in Cheltenham was circular.

I got my call-up papers for the army, did my six weeks primary training at the DLI HQ at Brancepath, was told at the end of the course that I was to join the Intelligence Corps, and suffered ridicule from my fellow recruits who were eager to get themselves killed in battle a.s.p. with a fighting regiment.

Off to Wentworth Woodhouse, supposedly the longest country house in England and then the Intelligence Corps Training Depot. Eight weeks cleaning a first-world-war bayonet scabbard which was issued to me in an oil ridden condition, riding AJS motor-cycles over rough country and firing sten guns at passing crows. Great, I thought, they will want me to carry despatches between Eisenhower and Montgomery.

The Intelligence Corps was a hybrid organisation. I t had an impressive cap badge – laurel leaves either side of a rose, and its shoulder flashes were distinctively green, but in the 'proper' army it rated somewhere between the RAMC and the Pioneer Corps. It embraced two completely dissimilar functions – Field Security and Signals Intelligence, but both branches received the same induction.

At the end of my eight weeks' bayonet cleaning and TT racing I still had no clue as to whether my destiny was to be in the physical or cerebral areas until I received my orders to proceed to Bedford.

An Edwardian house facing the river, and a cool reception from a WOII of the Intelligence Corps.

"Sign here" – the Official Secrets Act was pushed towards me. I signed. "Now tell me. what is this?" he demanded, flaring his nostrils, digging into his holster and whipping a weapon across the desk.

"A revolver, sir."

"If you ever, in the whole of you life, so much as breathe a word of what you are now going to be engaged in, it will be used to extinguish you. Do you understand?"

I did.

He put the revolver to my forehead, cocked it and pulled the trigger.

"Missed," I unwisely said.

"WHAT did you say?"

"Missed, SIR," I corrected.

Eyes bulging with rage, he retreated to his desk, opened a drawer, slung a large landscape-shaped exercise book in my direction and said "get on with it next door."

Two points: first – I got no help from my keeper in even understanding what it was all about. I had to deduce that I was expected to decode material, essentially employing frequency counts, graduating from simple substitution, through Playfair to more advanced systems. I did it, but with no great aptitude. Second – I never did reveal – not to my wife, nor my children, or to the non-plussed colonel of the TA tank regiment I subsequently joined, and who quite reasonably expected details of my previous army career, not to another living soul what I had done during my military service, until Bletchley became public knowledge in the eighties.

I was posted from Bedford to Bletchley and walked daily down from the army camp in the fields about the Park to the Yugoslav hut in the main complex, was given two weeks to learn basic Servo-Croat from a grammar, deciphered some corrupt text relating to the state of Sgt. Pavic's boots, the lack of cigarettes and the state of the donkey's left hind leg in a cave in Slovenia and in May 45, just as the war was ending, was posted to newly occupied Austria, where I saw out my service at Schloss Pfannberg, near Graz, reporting similarly exciting intelligence about the doings of Chetnicks, Titoists and other mysterious Slav groups to heaven whom in UL. Over fifty years later, no doubt GCHQ is providing Paddy Ashdown with almost identical pearls of intelligence.

I spent some six months leading up to VE Day at Bletchley Park and they are as vivid today as then. Imagine a nineteen-year-old ex-boarder from a bleak northern school, totally sex-starved and, due to wartime conditions, with miserable scant previous social contact, suddenly thrown into a ring-fenced enclosure where five hundred gorgeous, luscious, black-stockinged nubile WRENs roamed the large NAAFI hall and the surrounding rhododendron bushes. It was as if I had died and gone to heaven. There were, I think, five wrenneries dotted around Bletchley and particularly etched in my memory is the long walk along the tree-lined drive to Woburn and also an all-night forced route-march to another country house ten miles south of Bletchley escorting a different damsel in distress who had missed her coach. Only half as bad for her – I had to hike back just in time to tackle some scrambled Serbo-Croat at eight a.m.

So much for my career as a Bletchley cryptographer. A small matter in terms of world war II results, but for me an awakening experience, marked by sealed lips for as long as it took.