We picked up the key to the caravan, let ourselves in, ascertained the phone signal situation (none) and went to the beach. Polzeath beach is the kind of bucket-and-spade beach Janet and John’s Mummy and Daddy might have chosen for their annual holiday. First, soft white sand ideal for burying Mummy;  then a broad shining plain of hard, smooth sand, ideal for sandcastles, dam projects, or tunnelling to Australia; then gentle inch-deep wavelets — spent rollers — for toddlers and oldies to paddle in. Then flags. Then thundering surf crowded with Neoprene figures, all shapes, sizes and ages, some of them screaming, and riderless surfboards flipped skywards; each successive wave a chaotic and exhilarating drama.

We were an all-male, three-generation line-up this year: me, my boy and my boy’s two young sons. At the entrance to the beach all save my boy took off our socks and shoes and stuffed them into our bucket. Four abreast and squinting into the brightness, we progressed pale-footed across soft then hard sand towards the line of surf. My boy was depressed and preoccupied. His younger son was hanging on to his hand, grizzling. His elder son, however, was prancing ahead, shrieking ecstatic gibberish, and dancing dementedly in every rock pool. I saw only one item of litter: a Moët and Chandon champagne cork.

We possessed neither wetsuits nor boards, but we were equipped with the aforementioned bucket, blue, and a bright red spade. So we scouted some low, mussel-coated rocks, found a suitable cockpit-sized declivity, and grandad excavated thick, enclosing ramparts, so that when the tide came up, we could stand behind them and calmly defy the sea, until finally it breached and overcame them, whereupon grandad would do his startling impression of a German U-boat klaxon signalling action stations, and we would scramble to safety over the rocks.

While I laboured, my boy sat on a rock, rolled a fag, checked his phone again, found to his surprise that he had one bar, immediately made a call, and had an increasingly sharp altercation with his ex-partner for ten minutes, while his younger son clung to his trouser legs and cried. A smooth-faced young lad tripping over the rocks saw my effort, stopped, and said, ‘That’s what I call not bad, actually.’ I topped off the ramparts with a castellation of mud pies and we took up our positions within.

A calm, the first of our holiday, descended upon us. United behind our enclosing wall, we silently contemplated the encroaching waves, each of us closed off and occupied with our own private thoughts and fantasies. The lip of an advanced wave tipped into the moat, filling it, and withdrew. At the same time an elderly man, all head and earlobes, tropical tan, effete calves sticking out of the bottom of his wetsuit, and that invisible patina of class and authority, making an orderly retreat from the incoming tide, stopped, impressed perhaps by our Buddha-like impassivity as much as by my ramparts.

‘My word!’ he announced. ‘Magnificent! Will you be bringing up guns?’ They were on the way, I told him, not smiling. ‘What kind?’ he said. Howitzers, I said. He pouted in professional disapproval. ‘Too slow. Mind if I stick around as an observer?’ My boy rolled his eyes at me. His small sons eyed the man with profound suspicion. He took up a strategic position nearby, seating himself comfortably on a smooth rock.

A wave in the van of the rapidly advancing tide glided to the foot of our ramparts, filled the moat again and withdrew. I gave a loud burst on the U-boat klaxon. The elder boy shrieked for joy; the younger burst into tears. The big-ear-lobed man — I had him down as a retired sea lord or something —  made a fist and spoke calmly into it, as into the mouthpiece of a ship’s broadcasting system.

‘Remain calm. Work together. Remember your training. Steel your hearts. Honour your nation. You have been superbly trained, and for eventualities such as this. Nothing will occur for which we are unprepared. And at the first opportunity we will hit back, I can promise you, and with everything that we have. When we’ve finished with them, the buggers won’t know what hit them.’

I looked askance at this old man. His fist still to his mouth, he flashed me a happy warrior look with his eyes. The third wave undermined our redoubt, the fourth breached it, the fifth and sixth overwhelmed it, and we abandoned our precarious position, piggy-backing the children over the rocks. ‘Keep calm!’ counselled the authoritative voice through the curled fist. ‘Remember your training! Do your duty!’

Anybody who thinks our Prime Minister’s was slumming it by choosing Polzeath for his annual holiday couldn’t be more wrong. There he was in fact entirely surrounded by his own powerful social class, phone signal or no phone signal.