Queuing up to pay, she stood behind a bedraggled and scrawny young woman with a baby in a sling, a tiny girl strapped into the child’s seat in the trolley, a dummy in her mouth, and a small boy about Aggie’s age who kept tugging at his mother’s skirt.

‘Mummy,’ he said. ‘Mu-um.’

‘Not now, Jack.’ She was hauling objects out of the trolley and shoving them onto the belt: nappies, biscuits, sausages, tins of beans, oven-ready chips. Every time she stooped down, the baby half woke in the sling and whimpered. The woman looked wretchedly hot. Her hair was plastered to her forehead and there were circles of sweat under her armpits.

‘But Mummy …’ The boy gave an unmistakable, tight-legged jiggle.

‘Not now. How many times do I have to tell you?’

‘I’m desperate.’

‘What?’

‘I need a wee.’

‘Oh God!’

‘It’s not my fault.’

‘I asked you before if you needed a wee. Hold it, can’t you?’

‘Shall I take him for you?’ said Irene.

‘Mummy.’

‘Let me take him.’

‘Hold it!’ she said to the boy, ignoring Irene. ‘I’m nearly done.’

She went to the other end of the check-out to stuff her shopping into bags and sling it back into the trolley. The boy jiggled some more. He looked close to tears. Irene smiled at him encouragingly but he stared at her as if she were an object he’d never seen before and didn’t recognize at all. His mother paid in cash. She handed over five ten-pound notes, then scrabbled in her purse for coins. Laboriously, she counted out four pounds, most in ten-pence and twenty-pence pieces. Then she started counting out coppers, but was still short by twenty-eight pence. She scrabbled in her purse as if the money would miraculously appear, then dug around in the bottom of her bag where she found a five-pence piece. Irene wanted to offer her the change; she couldn’t bear to see the little boy crossing his legs and biting his lips, staring at his mother in desperation.

‘I’ll have to put back the crisps,’ she said. ‘That’ll do it.’

The woman keyed in the reduction. The little girl in the trolley seat spat out her dummy and started to cry. The baby in the sling joined in, opening its mouth so Irene could see its pink tonsils. The boy suddenly relaxed. He ducked his head down to hide his tears and sidled up to his mother, pulling her skirt again.

‘Wait!’ she snapped. ‘All of you. Can’t you see I’m almost done?’

‘I couldn’t help it,’ he whispered. His trousers were dark down one leg.

‘Oh you haven’t. I told you to bloody wait! This is the last straw, it is!’