But we live in a new world now and, open-minded though he is, Sir Bonar evinces no sign that he recognises that fact. The paradigm has shifted.

We at the top of the Civil Service now see ourselves as investment managers mandated by our clients to earn the highest possible return on their portfolios. For decades it has been clear that trading is a mistake. Trading takes time, settlement goes wrong and incurs fees and there is always the outside chance that securities sold will subsequently go up and securities bought go down.

These unnecessary risks are avoided entirely by re-shaping the portfolio, not by buying and selling – “doing something”, as Sir Bonar quaintly calls it – but instead by writing a series of under-the-counter (UTC) contracts which can more efficiently nudge the portfolio into the optimal profile selected by scenario development.

This approach is now so obvious to portfolio managers that they might as well have imbibed it with their mother’s milk and it is only the antediluvian Sir Bonars, scripophilists to a man, who imagine that there are still safety deposit boxes with physical share certificates lodged in them in vaults all over London – or rather, under London.

That, and strip trading, also taken in with their mother’s milk. Take a look at an old-fashioned share. What does it comprise. Some capital value. A bit of income. Various flavours of risk associated with interest rate fluctuations, exchange rate differences, maybe a bit of market risk and a dollop of moral hazard. Each of these can be “stripped” out and managed separately. Not traded, like the US Treasury strips of yore, but managed, UTC.

Sir Bonar’s particular interest today, security, is no different. The security strip of our portfolio – the UK – can be managed by expert derivatives traders, young men and women trained, in the main, by the maths departments of our better universities, and armed with supercomputers.

Keeping the UK on the balance sheet holds back performance of the portfolio. High returns can only be earned by gearing up. What we have done is to take the security flows as a whole, discount them back to a net present security value (SV), parcel them up into easily understood units (“people”) and then write contracts on them. Simple financial engineering at its best, the balance sheet is liberated, the old, slow market involving conception, gestation, parturition, etc … is lubricated into a fast-moving modern, highly liquid network (not soup, by the way, whatever Sir Bonar thinks), turnover goes through the roof and our fees follow it.

These contracts need to be insured, naturally, and so a further network of Security Default Swaps (SDSs) has grown up to underwrite them and has itself become an even bigger market. The old problem of how to lay off risk in unwieldy great slabs has been solved elegantly with modern technology so that it is spread thinly and manageably throughout the world.

Limpidly clear to the average teenager of today, it is doubtful whether Sir Bonar will ever come to grips with the modern world of the security services. Never mind. He is still an agreeable, clubbable companion and, it must be said, a usefully avuncular front man, a latter-day Mr Pastry, inspiring, as he does, endless popularity and jovial confidence among the simple SVs of the modern world.