Suedehead:
As an aside.
Are they a legal requirement?
I know that if a light is fitted,it must be working . . .
Not true - the only ones which must work are those which are required to be fitted. For example, reverse lamps have to comply with the Road Vehicle Lighting Regs, but as they are not required to be fitted, no offence is committed if they don’t work.
DRLs are not yet required on all new vehicles - just on all new models. A brand new vehicle built under a pre-existing type approval (pre 2011 for cars and vans, pre 2012 for trucks and buses) will not be required to have DRLs so it won’t matter if they don’t work (some manufacturers may fit them to older models still in production purely for marketing purposes).