‘Almost,’ I reply, and we are both in grave danger of cracking a smile.

‘It’s very busy,’ says Dad. ‘I came here a lot as a boy. And your mother and I used to walk here from Clerkenwell.’

‘Did you?’ I can’t imagine him and Mum walking round here, looking at the boats. I can’t imagine them doing anything I haven’t seen in photographic evidence or viewed through the prism of my own memory.

‘Yes. She liked it a lot here.’

‘Right.’ I don’t want to talk about her. He never usually does either. But maybe he is flicking through the photo album of his memory, selecting images he likes. Does he like it here? I wonder. He hasn’t really said. There has been a lot of grumbling and complaining. A lot of sighing. Still, we’re here. We’re out again. Without accident or incident, so far. Except revolting ice creams.

Another barge sounds a jovial horn. A child shrieks with delight at an over-enthusiastic dog. And a dragonfly levitates into view and hovers over Dad’s thigh.

‘Oh, a dragonfly,’ I say.

‘A dragonfly?’ says Dad. ‘Describe it to me please, Prue.’

‘Oh, OK. Well, it’s blue and it has four wings and—’

‘What shape is it?’

‘It has a long thin body, like a pipe – it looks too long for its wings to ever be able to hold it up. The body is bright blue with black markings. Its wings are almost see-through. They have veins in them, like leaves.’ I’ve never looked this closely at a dragonfly before. It really is beautiful close up.

‘What else?’ Dad is frowning, like he is trying to imagine.

‘Well, it has a blue head like a motorbike helmet and a bulbous sort of blue body underneath and … that’s about it, really.’

Dad listens and nods. The dragonfly hovers for a minute then helicopters off, back to the canal.

‘It’s gone now.’

Dad nods again. ‘That was a good description. You did a lovely picture of a butterfly once,’ he says, ‘when you were a kid. Didn’t you win a prize for it?’

‘Yes, I did,’ I say. I liked art. As well as the benefits of it being a quiet activity in school – heads bent over desks, less bullying jibes – I liked the pencils and the charcoals and the pastels and the paints. I liked the way a brush wet with cobalt blue or vermillion red felt when it was stroked on to cartridge paper. How colour and lines transformed a blank paper into something new.

‘You were a talented kid. So was Angela. All that craft stuff.’

‘That was mainly her. All that terrible jewellery we made from those sets she got for Christmas,’ I say. ‘That weaving loom …’

‘Yes, that’s right. Some of that stuff was good!’

‘Ha, hardly.’