British Dispatch Rider helmet Laces

[M.E.E.]

Hi, sorry if this is a silly question but was there a set length or colour for British dispatcher rider helmet laces? I recently bought a new old stock dispatch helmet but it is missing its lace so I plan on tracking down some old stock laces but wanted to know what was most likely used. I have seen flat, round, black, brown, and green laces from pictures but I am not sure what it would have been issued with.
Thanks in advance.
Mark

[tinlid]

I'd go for black round.

[M.E.E.]

Appreciate the info and picture, I will use it to figure out the lace length I need.