Help dating BSA M21

[SpannerMan123]

Hi everbody

I'm looking for a little help dating a bike I've just bought its a - BSA M21
I've been told it was built in 1954 but I've nothing to confirm that.
Details below :-

Frame number BM20 728
Engine number BM21 6271
Reg number RNA 440

I also need to know where/how to apply for logbook??

Thanks for your help
-Ray

[Bess]

Hi,
    Check with this pdf:

Best wishes...

[JulianS]

RNA440 is a 1955 Manchester plate.

But looks like it is on a VW now.

https://vehicleenquiry.service.gov.uk/?_ga=2.250834245.2127938827.1574528447-444782083.1564223722