Yes, you can certainly be in Belmarsh on remand if you're accused of a terrorism offence - why was he placed elsewhere? One for the enquiry, I suppose.
I've been looking at the route, and wondering if the lorry had other drop offs, because otherwise (and other Londoners' views on this would be interesting) it looks a bit odd.
I think leaving the prison and turning south is (I think) currently the only way to go, as there have been roadworks at the railway bridge on that road and it's been closed to anything bigger than a bicycle (and probably still is).
So then going round and on to Trinity Road is logical. But if heading for Putney, why didn't they turn left at Wandsworth Common Northside, instead of going down to the Wandsworth Roundabout? Another delivery, I guess (assuming no complicity from the delivery firm - but is that a wise assumption)? Because after the roundabout, they headed straight back into the Wandsworth gyratory system (which is exactly where you'd end up if you'd turned left earlier - again fellow Londoners, is there a disadvantage between going in to it from East Hill, compared to coming at it from the north?) Perhaps the police aren't releasing everything about the van's movements and stops.
Sorry for the armchair Marple-ing. Where he got off the lorry probably doesn't make much difference in the greater scheme of things!!