‘You’re right,’ Jamie agreed. ‘We’ll simply explain to them that it isn’t polite to record your neighbours having sex.’

Kirsty smiled, despite herself.

‘They’re definitely in,’ she said, after Jamie had knocked on the door and they had waited ten seconds without a response. ‘I can hear the TV. Knock again.’

Jamie did, rapping on the wood three times. There was still no answer.

‘They don’t want to talk to us,’ he said. ‘They must have seen it was us, but they’re hiding.’

‘Why would they do that?’

‘I suppose they think we’re going to have a go at them. No, actually, I’ve no idea what they think – I don’t understand them at all any more.’ He walked away and started to go up the steps. ‘Come on. I don’t want to waste any more of my time.’

Kirsty followed him. He walked purposefully into the living room and picked up the phone. ‘I’m going to call the police. Tell them we’re being harassed. It’s got to be illegal, recording your neighbours having sex. Actually, it must be illegal recording your neighbours full stop.’

Kirsty stepped in and took the receiver from him. ‘Jamie, if you get the police involved it will only make things worse. We’ve still got a chance to sort this out.’

‘But they won’t even answer the door to us.’

‘So let’s write them a letter. That’s obviously how they want to communicate.’

She opened a desk drawer and took out a writing pad and a pen. Then she sat on the sofa and chewed the end of the pen thoughtfully.

‘What are you going to put?’

‘I don’t know. You’ll have to help me. I haven’t written a letter on paper for years.’

Jamie sat beside her and, over the next hour, they composed a letter, Kirsty holding the pen because she had the neatest handwriting (Jamie had been using a keyboard to write everything for so long he had almost forgotten how to do joined-up writing), with Jamie looking over her shoulder, making suggestions.

Dear Lucy and Chris

We have to confess that we were surprised by your letter. We class ourselves as your friends, as well as your neighbours, and we would have thought that if you have a problem with the levels of noise (of whatever sort) coming from our flat you would have felt able to approach us in person. We could then discuss the situation as friends – and as adults.

As it is, the tone of your letter is very unpleasant, and we also find it difficult to express how unhappy we are that you recorded us. We insist that you delete the recording and destroy any physical copies you’ve made.

‘Should we state that if they don’t we’re going to go to a solicitor?’ said Jamie.