a small film re early crash helmets there was a bike not sure what model as you don't get a full view of the bike but the C number was fairly visible it was C 4327567 the 6 could have been an 8

email (option): roger.beck@node6.com

Do you know what the film's called or when it was on TV?

email (option): horror@blueyonder.co.uk

It was part of the BBC Watchdog Test House series. It was on the box yesterday and is on BBC iplayer at the moment. Unsure as to the name of the film the clip is taken from. A title does appear but I believe it is for a later post war programme. It is at around 10.50 in to the clip.

http://www.bbc.co.uk/iplayer/episode/b03zj9ww/Watchdog_Test_House_Episode_15/

I agree with the interpretation of the number. Except the next to the last digit could even be a 0, but I think 6 is the most likely.

According to Chilwell list, it would have been a Royal Enfield Motor cycle solo. 250cc or 350cc depending on the exact number.
All in same contract C7945

Cheers

email (option): wd16h@telfort.nl

Had a look at the link to the Watchdog programme.
The two guys riding down the hill in film are in Brewhouse Hill, Wheathampstead, Hertfordshire. Helmets Ltd was based in this road. A bit further down the hill on the right-hand side.
I think they produced the Cromwell range of helmets in the 1970's