many lights don't as numbers sold in UK relatively small so manufacturers don't bother to put them up for test. light is legal whether or not UK spec compliant.

It seems flashing lights are no longer regarded by Police as unlawful. Hopefully every one realizes that it is more noticeable to see a flashing light where the gap is in milli secs.

It is not marked to conform to a BS or equivalent, therefore it doesn't. Technical advice from CTC was (approx) that you are unlikely to be stopped or prosecuted if you have lights, but if involved in an accident, non-standard may count against you with courts and/or insurers.
BS is lagging behind technology so far now...

In the blurb on Wiggle, the product description says 'Standards: RVLR'.

This should mean that they are compliant with UK standards and regs per the Dept of Transport. Try these links:

http://www.dft.gov.uk/pgr/roads/vehicles/vssafety/regulationsforpoweredtwoandt4564

http://www.ctc.org.uk/desktopdefault.aspx?tabid=4071

http://www.cateye.com/sites/cateye/upload/manuals/en/LIGHT%20POS%20USA%20081009.pdf

I use them on the road and not been stopped yet.

Can't see any references on the packet though

You need the H-34 Flex-Tight bracket. This has the internal clip for the EL-135, and also the external notch for other lamps.