‘We like to think we are doing our bit,’ Lowgreave said, as he risked a sip of the coffee. ‘It’s not glamorous work, but we save thousands of tonnes of valuable product from going to waste. The stuff we can’t make use of goes in sealed railway containers across to the Bristol Channel. It’s burned to produce electricity. So it’s pretty green.’

Gillard set aside his less-than-single-use coffee, probably the only drink worse than any police beverage, and asked to be shown the retrieved mobile. It was on Lowgreave’s desk, in a clear polythene bag. A standard Samsung model, clearly contaminated by some sticky substance.

‘Is that how it was?’ Gillard asked.

Lowgreave nodded and brought in Gladys Olewando, who had answered the phone when Gillard had rung it. A very large black woman, on whom three square yards of hi-vis was utterly redundant, she said she had retrieved the phone from the magnet.

‘Do you get many phones in the rubbish?’

‘Maybe half a dozen a week,’ she said. ‘The magnet doesn’t do them any good, but this one was on a long streamer of metal cans and coat hangers dangling beneath.’

‘And you’re quite sure there is isn’t a body?’ Hoskins asked.

‘We dumped the entire container out onto a big plastic sheet,’ Lowgreave said. ‘That is what we always do on these occasions. In the old days, I would have just sent the guard dog in there. He’d have found a body in no time. Anyway, Gladys and Mick went through it. No body, no body parts.’

‘Where did that hopper come from?’

‘Ah, now. Most of what we take in here is household waste from the Borough of Brent. But we have a contract with Network Rail to take their mixed consumer train waste from Waterloo and Paddington, two consignments per day. This came from the Waterloo truck.’

‘That makes some sense,’ Hoskins said.

Lowgreave passed across a business card. ‘That’s the bloke you need to talk to at Waterloo.’

An hour later, the two detectives were standing looking out from a high window over the enormous concourse of Waterloo Station. With them was Phil Perkins, the Network Rail recycling manager. He pointed to an arriving train on platform six. ‘There you go. That’s the slow Guildford service, come in via Cobham. The fast ones go via Woking. The procedure is that the mixed waste from on-train bins is picked up by contractors and then goes into a hopper, which is wheeled out to the waste trucks.’

‘Does anyone go through it at this point?’

‘No, not really. There’s always a security check, because of the possibility of explosive devices being residual in bins, which used to happen in the old IRA days. So our operatives always take a visual glance in the bin bags, especially if they feel anything unusually heavy: batteries, wires, stuff like that. Unfortunately, although we have plans to ban concessionaire use of single-use plastics in-station by 2020, and are already providing refill points for plastic water bottles, the issue of mixed waste in litter bins, whether on-concourse or on-train, is still moot,’ he said, sucking his teeth. ‘The problem is that coffee cups, carton lids, straws, drinks bottles and so on can be recycled in some cases, if they are clean. In practice, approximately 38.4 per cent of bins are dreg-contaminated and consequently recycling non-compliant. It’s simply not cost-effective to deal with it.’