For the third time in five minutes, I hung up. A Google search on my mobile told me Pollard and Clarke was a law firm based in Holland Park, just round the corner from Mel’s office.

They specialised in family law and divorce.

I felt winded, like I’d been punched in the stomach. Mel had been unfaithful, she had deceived me – but to have lawyers involved gave a ring of finality to it. I leaned against the side of the booth, my head on the glass, a hard pain in my chest. How was I going to tell William what was going on? How was it possible for a four-year-old to understand that his parents were –

There was a metallic tapping on the side of the phone booth. A pasty-faced teenager was knocking on the glass with the edge of a pound coin.

‘You finished mate, or what?’ His voice was muffled through the glass. He had a black baseball cap perched on the top of his head with a metallic green cannabis leaf on the front.

I pushed open the door.

‘What?’

‘You finished?’

‘No.’

‘How long you gonna be?’

He was wearing a dark hooded top, jeans hanging halfway down his backside, showing off four or five inches of his boxer shorts. A sparse scattering of stubbled acne along his jaw, a toxic blend of stale joints, body odour and unwashed clothes hanging around him like an invisible cloud. There was something familiar about him. Four others, dressed almost identically, lounged on a bench a few yards away.

I said: ‘As long as it takes.’

He turned to his four mates, grinned. Turned back to me.

‘Get on with it, yeah? Been waiting like, ages, innit.’

‘Really? I’ve got an idea for you, then.’

‘What?’ His head wobbled slightly side to side, like a combative guest on The Jeremy Kyle Show. He looked jumpy and strung out and I had a pretty good idea why he’d want to make a call that couldn’t be traced. ‘What idea?’

Most of my professional life as a teacher had been spent taking low-level disrespect like this on a daily basis, without being able to do anything about it. At least, nothing effective. It was always take a breath, take a minute, be the adult, have a word – not that that ever achieved anything. But I wasn’t a teacher today. Everything was boiling up inside me, like a chemical mixture about to explode.

‘How about,’ I said, ‘you turn around, pull your fucking trousers up, and fuck off. ’

I expected him to square up to me, react, get angry, start pushing or shouting. But instead he looked taken aback, utterly surprised, as if he’d never been spoken to that way in his life before.

‘All right mate, chillax, yeah?’ He backed off, swaggered over to his friends on the bench who were laughing and jeering, calling him out for being dissed in public.