Most people ignore their blood pressure because hypertension is asymptomatic. In other words, there are no symptoms until you drop down with a stroke. Ten years ago I was walking along and suddenly saw a little spot in my vision. It turned out to be a retinal thrombosis. It was a tiny warning, but a warning nevertheless. Both my parents died of strokes, so high blood pressure can be a problem for me.
In London, I had a full cardiovascular check and the doctors told me that I had high blood pressure that was controllable with drugs and regular check-ups. I decided to monitor my own blood pressure. In those days, you had to buy a doctor's kit, with a cuff and stethoscope. You would spend lots of time learning to recognise a change in pulse beat and discern systolic and diastolic moments.
I moved on to a cuff plus electronic display which had all sorts of requirements - your arm had to be straight and supported along its whole length. Then I came across a Japanese-made digital blood pressure device called Lumiscope, costing about pounds 40. It fits in your pocket and measures the blood pressure in your left index finger; you stick your finger in, hold the device at heart level and press the start button. Thirty seconds later you have your BP. Anywhere, any time.
There is one other time when technology would have been useful. When Tim Philby, the British traitor who defected to the KGB, gave his first interview to me, I was told I would be welcome in the following order - wife and notepad. Six days of interviews had to be written in longhand. Perhaps they wanted to be in a position to deny things that were said.
What will strike viewers about the TV programme The Spying Game is how old-fashioned the technology was during the Cold War. There's been a dramatic change since then. The main change is that voice communication is no longer secure. The US national security computers are monitoring conversations with keyword interception - if we mention the "Islamic bomb" or "terrorist", the conversation is then monitored.
Interview by Jennifer Rodger
Philip Knightly appears in the Channel 4 series `The Spying Game: Tools of the Trade', beginning Saturday at 7.30pm