I think the parent means that the person who is driving past the LSE with his jammer is less likely a delivery driver, as they are under close scrutiny but rather anyone else.
Might as well be anyone who'd rather not be tracked if they can help it. I can imagine perhaps a VIP or even an organized crime member who prefers their car free of GPS trackers when they drive around town visiting associates.
It's even less likely he jams signals where ever he goes and LSE just happened to notice it. His company would be very curious why he was disappearing. They can pull him on a screen and watch when he goes in and out of range. It would happen only to him, in whatever vehicle he happens to check out that day. A driver would have to be far more clever than that.
The article states "timestamps on trades made in financial institutions can be affected" There's your likely culprit; someone who for whatever reason needs to affect timestamps.
I think it's likely a driver who is constantly jamming his GPS. I have seen this in work with the FAA. A driver will go past the airport or park and deliver something. We see a temporary GPS outage which have traced back to delivery drivers in several instances. I imagine their company assumes their GPS equipment is broken, but still lets them drive.
It seems like an airport would be pretty eager to identify and prevent this so it doesn't go on. Maybe the London Stock Exchange doesn't care as much, but if it messes with trades?
I'm curious as how this disruption could be used in a financial scenario. If you disrupt the GPS for 10 minutes, would the timestamps really go that out of whack?
And more importantly, will they go out of whack in a way that's useful? Being able to shift the timestamps a few microseconds could be quite valuable if you can do it only to your order gateways (and ensure it's in the correct direction) but "jamming GPS" doesn't seem to get you that. I'm not going to say there's nothing it could be used for, but it's not jumping out at me.