My father assured him more than once that Warsaw would be protected by international convention, that the Germans would behave as they had done in the First War, harshly but correctly. Much as we loathed the Nazis, we took German decency for granted. Had anyone imagined the horrors that were taking place from invasion day onwards – round-ups and mass murder in baroque town squares, packed synagogues put to the torch on Yom Kippur, 24 September 1939 – my days with Dovidl would have been shrouded in mourning and I could never have shared with him the rambling discoveries of that dilatory London autumn.

I designated myself to be his refuge from anxiety, frantically planning excursions to distract idle thoughts. Panting on our bicycles, we rode up Highgate Hill, only to be denied entry to the great Victorian cemetery with its grave of Karl Marx, on the absurd grounds that we were too young.

‘You have read Marx?’ said Dovidl.

‘A short extract, he’s very dry.’

‘Like a rabbi’s kiss,’ he flashed, and I gasped at his irreverence.

We leaped on our bikes and freewheeled down the hill, narrowly missing a milk float, from which Dovidl coolly lifted two pints while the stripe-aproned milkman went round to calm his horses.

‘You know, it’s going to be all right,’ I told him, arm around the back of a bench on which we sprawled to glug our booty.

‘In England, perhaps,’ said Dovidl. ‘Provided you win the war. In Poland, not all right. Maybe people come through, maybe no.’

‘You are in England,’ I said sternly. ‘Your father sent you here. You have a job to do. The thought of you studying in safety will get them through the war. You will not help them by worrying.’

The steady clip-clop of the approaching milk float made a quick retreat advisable. Skimming along Archway, weaving in and out of sluggish traffic, we headed home in thickening mist that threatened to turn to choking smog. ‘We make good team,’ said Dovidl, as we turned into Blenheim Terrace. ‘I do job and you, Mottl, you take my mind away from worries. Together, we make it work.’

‘Does that make us best friends?’ I wondered, searching for some orderly categorisation.

‘Not friends,’ said Dovidl. ‘Something more.’

His studies with Carl Flesch ended abruptly, almost before they began. The old professor had returned from his Belgian spa to resume giving lessons at his West Hampstead studio. I accompanied Dovidl the first time, reading old issues of The Bridge in the waiting room while Flesch put him through his paces. As I browsed, a cadaverous young man strode in, the next pupil.

‘Josef Hassid,’ he said, extending a bony hand.

‘Mottl Simmonds,’ I replied, adopting a friendlier forename.

‘Did you see who that was?’ whispered Dovidl, as we left. ‘That’s Josef Hassid from Warsaw, a fabulous talent. He lives here with his father. Did you see? He said hello to me.’

‘We had quite a chat in the waiting room,’ I pretended.