Knowing the area where this incident reportedly occured quite well iwas curious to try and locate the area where the laser may have been shone from.
The track at the beginning of this thread shows a easterly departure from LHR 9R and assuming a standard Compton departure the captains estimate of about 8 miles from Heathrow puts the plane just south of Lego land themepark situated in the middle of the crown estate at Windsor. That would fit perfectly with estimates that the laser was 1-2 miles off to one side- ie to the north of track.
So I wonder if this was either an errant laser from a show or an employee testing/fooling around with one. They have a lot of laser shows there and it does seem a bit of a coincidence that this occured not just close to lego land but just the right distance to the south-so maybe just an error on an operaotrs or technicians part.
Not an ideal location for laser shows though being under SID tracks from both easterlyand westerly departures from LHR-presumelably they normally operate restricted power versions