‘The drones are quadcopters,’ said Campbell. ‘Thirty minutes flying time, and a range of three or four miles. Fitted with GPS and a bloody good HD camera. The remote control can work with a smartphone, which displays the live video feed. And they can be preprogrammed for independent flight.’

Gabriel took over. ‘In summary, we know that Abu Mujahid picked up four recruits from London, drove them to a remote retreat in the Lake District, ordered and collected two drones from Amazon, and has now left the Lakes.

‘We know he has additionally collected a cache of weapons and explosives at a warehouse in Burgess Hill – we presume similar to those uncovered in Canada – and an army rifle from our army sergeant in Hedingly.

‘In the last forty-eight hours, we have gone from being largely in the dark about Abu Mujahid’s objectives to having a much clearer idea of his potential threat. Ladies and gentlemen, we need to continue our progress and find the target.’ That last line was mostly for Tennant’s benefit. No harm boosting the team in front of the boss.

‘Maybe the drones are to disrupt or attack an airport?’ said Campbell. ‘Remember the chaos that drone caused at Heathrow a few years back.’

‘Not convinced that’s his style,’ said Gabriel. ‘He will want to maximise impact, kill as many as he can, and do it in a spectacular way.’

‘Could he fly them into a plane then?’ said Skeffington. ‘A bird can rip apart an engine on its own. What would a chunk of metal and plastic do?’

‘I think the impact is too unpredictable,’ said Tennant, speaking for the first time. ‘You might take out an engine if you were lucky, but there’s no guarantee of bringing a plane down.’

‘Agreed,’ said Gabriel. ‘And he’s got explosives – we know that. He can use them as flying bombs. We’ve seen ISIS do that already in Syria with similar drones. He could get them over any security line he wanted.’

‘Surely that kind of drone wouldn’t have the power to lift explosives?’ said Skeffington.

Campbell shook his head. ‘These would. And you wouldn’t need much explosive to cause havoc.’

‘It’s a theory, and it’s something to work on,’ said Gabriel. ‘Eva – have you got the list?’

‘Yes, ma’am,’ said Bose, who had walked into the room a minute earlier and was hovering on the edge of the conversation. ‘The drones narrow down the potential targets considerably. Abu Mujahid would need an open-air event – or at least a large crowd gathered outside.’

Gabriel took the paper. ‘Jesus – there’s a hell of a lot on over the next few days.’ She read from the list. ‘A marathon in South London tomorrow morning. A Pride march at noon in East London. An England football international at Wembley against Hungary, kick-off at 3pm. And the Calcutta Cup on Sunday at Twickenham.

‘Another thing, if Abu Mujahid is using drones, then he’ll be operating from a secure base, with access to the outdoors. And not overlooked. Somewhere relatively close to the attack scene. We’ve got two jobs – find the target, find Abu Mujahid.’