DIY Rear Thumb Brake

[Negrogrande]

So I looked in the GCRs
and there was no specific mention of a foot operated rear brake being needed.
15.1.2 Brakes
15.1.2.1 At least 2 efficient brakes must operate
independently of each other on the front
and rear wheels.
15.1.2.2 Front brake caliper mounting bolts to be
lockwired in the tightened position

I might give building a thumb brake a go, at worst I can always change it back