If you've seen Nanny McPhee and the Big Bang, you've no doubt caught the shots of the girder-forked, olive drab, vintage motorcycle with a sidecar. Turns out, the good nanny rides a bike that appears to be a 1948 or older Ariel. The trailer can be seen on YouTube (this link will skip you to the Ariel). Zimbio.com reports that a 6 foot tall stuntman did the actual stunt riding.

https://hermajestysthunder.blogspot.com/2011/02/nanny-mcphee-rides-ariel.html