In the main I simply don't ride at night, so don't need lights, I think even if the law does not allow flashing lights, these identify to the car driver that it is a bike, so still like flashing lights, what I am considering is when for example I get a puncture and so am delayed, so I have not got off where I am riding before dusk.
The mud guard

means any light below seat hight is useless, and above seat hight is not the bike and for 4 inches below the seat likely any coat will also obscure any light. So I have two arms,

that when folded will be on the outside of the bike so bottom arm is useless as top arm will obscure, and it needs to be on top of top arm not to side as once folded likely will get damaged.
So I want a lamp mounted some thing like this.

However not found a lamp with mounting brackets that would allow it to be mounted in that way, old dynamo lamps

would work, but then need to get power to it, I assume I can tap into front lamp but seems likely 48 volt, but I can't be alone, loads of people must want to do the same, and I just can't believe there is not a cheap read lamp which I can mount on that near horizontal bar, with one would hope the correct BS number making it legal in UK.
I am sure I can make a lamp bracket, but why re-invent the wheel, this must be a regular requirement so would have expected an off the shelf lamp which will do the job.
And yes I know there have not been bicycle dynamo for around 70 years, alternators replaced them years ago, but still call it a dynamo even if it is an AC output.