UK Police Test 'Temporarily Blinding' LASER
esocid writes "Called the SMU 100 it costs £25,000 and sends out a three-meter 'wall of light' that leaves anyone caught in it briefly unable to see. Designed by a former Royal Marine Commando, it was originally developed for use against pirates in Somalia. While tasers and CS gas work well over short distances the laser is said to be effective at up to 500 meters (1,640ft). Being targeted by the beam has been compared to staring into the sun before being forced to turn away. Paul Kerr, managing director of Clyde-based Photonic Security Systems, which came up with the design, said 'If you can't look at something you can't attack it.'"
Blinding laser weapons are specifically mentioned in the Convention on Certain Conventional Weapons annex of the Geneva Conventions.
See: http://en.wikipedia.org/wiki/Protocol_on_Blinding_Laser_Weapons
And yes, it does make a specific distinction between temporary and permanant blindness, so this thing is almost certainly legal as far as this particular protocol goes.
I should point out though, that the UK police have never even resorted to using water cannons outside of Northern Ireland, and use of riot equipment is a very serious political issue here. Breaking out the doom rays on a crowd of protestors is not going to happen lightly, and if it did happen, it would not be brushed off or ignored afterwards.