Is their a legal requirement on the size of headlights?

Not as far as I know but surely all headlights must comply to some European or British Standard. What specifically are you thinking of using?

the smallest and lightest i can find. Demon Thieves have some very small (3" lights used on Motorbikes that also have side lights built in. If they run the right bulbs then hopefully they are the ones. But will motorbike lamps have the right lens for car use?

No they won't. (At least not for SVA). The beam pattern on motorcycle lenses is straight ahead, whereas UK cars beam pattern is to nearside.

Chances are, you could get away with fitting them after SVA but whether they are suitable or not is for you to decide.

this is the bit where your meant to go thru other threads. GTS Cougar do some very small lights, so will email them to make sure they are SVA approved. They also look paintable which helps!

IIRC the smallest SVA approved headlights are 5.75" There has been some talk in the past, of smaller diameter headlights passing SVA by rotating the lens of a motorcycle headlight to give a beam pattern to nearside but not so sure myself.

SVC.co.uk are currently searching for smaller lenses with SVA approved markings and correct beam pattern for UK and will tool up to make the housing/casing to suit, if and when one can be found. GTS do have smaller headlights available but the last time I looked, it didn't state they were SVA compliant. However, things may have changed.

Phil

Yep, I agree 100%. SVC every time.

Phil