‘It depends how complex they are and how clever he has been. I don’t think Anderson’s people have examined the link between Arrowsmith and Slater, they’re looking higher up the food chain.’

‘Look, all we need is proof he paid Slater outside normal channels,’ Gillard said. ‘Either a withdrawal of cash or a bank transfer.’

‘It would be easier to find it at Slater’s end,’ Shireen said. ‘He’s probably less financially savvy than Arrowsmith, so we’ll look for a big wodge of money coming in from an unusual account.’

‘How long might that take?’

‘Days to find it, but weeks or months to piece it all together enough to satisfy the CPS. It’s never quick.’

Gillard nodded. ‘All right. I have a plan. We release Arrowsmith on police bail, and keep him and Francesca under surveillance. Phone taps, the full works. Slater is bound to contact him, or vice versa.’

‘Arrowsmith is pretty clever. First thing he’ll do is get himself a new phone.’

‘I’m sure, but it’s the best we can do. In the meantime I’m going to dig around Slater’s place of work.’

The search for Ray Slater was intensified. Now the Met had finished searching, Gillard made time to take a look at Slater’s small office in West Croydon, and his modest home around the corner. Surveillance teams had reported no significant visitors to either location.

Slater’s office was above a Turkish barber shop, which on a Saturday morning was packed with an ethnically diverse clientele. The office entrance was easy to miss, hidden between the barber’s and a Chinese supermarket. The door was neat and tidy, with a small surveillance camera above and a buzzer, plus a brass plate inscribed RAS Business Services. It would have been as discreet and obscure as you could get, except for the hefty Met Police padlock securing the place after it had first been raided. Gillard fiddled for the key in the envelope given to him by the surveillance officer, tackled the padlock and opened the door. He was dearly hoping that he would spot something that the Met Police had missed. They’d raided the office, Slater’s home, and interviewed nearby relatives in Croydon. There was no sign of Slater’s whereabouts. Nor of his wife, which made Gillard think they might be planning a runner.

Still, the Met claimed to have their passports. There was nowhere for them to go.

The stairs were uncarpeted, and the wallpaper a tired beige woodchip. As he climbed Gillard got a whiff of unemptied bins. A piece of lino ran from the stairs to the office door, which was cracked from top to bottom from what appeared to be an enthusiastic use of the police ram. The padlock here was superfluous. The frame was so splintered a toddler could have barged in.