In my 150….
Our dear Government (peace & blessings, etc.) has put the Inspection Manual for Classes 1 and 2 Vehicles here, for us all to enjoy:
http://www.motinfo.gov.uk/htdocs/
Paperwork-wise, evidence that import VAT has been paid is required, and also a certificate of newness unless one is content with a Q plate. That, as far as I recall from last time, is all.
I think making a motor vehicle road legal requires a bit more than a horn and a number plate. If it doesn’t the vehicle manufacturers are wasting a lot of money on type approvals and homologation!
For use on public roads other than night/IMC it will need an electric horn, a number plate and some paperwork. But we’re pilots, so we should be able to do paperwork… 
@Jacko, these pit bikes as shown are obviously not road legal – or do you intend to adapt them?
I’ve had two Bromptons since 2003, and carry them in my 150, and I just bought a third Brompton. They are the best choice for my experience.
On the subject of ground transport, I’ve determined that two of these pit bikes will fit easily in an MX-7 (and probably most full-size GA aircraft) after removal of the front wheels:
http://funkybikes.co.uk/shopexd.asp?id=76
At £399 they’re awesomely expensive (by Maule standards), nearly half the price of a used mountain bike, so if anyone else in Blighty needs one we could try to negotiate a group discount…
ATB, Peter.
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MX-7-180 N280SA
For the lazy ones: lightest electro-bike on earth (9.9kg)
http://www.vlec-cycles.eu/english//product_detail.php?id=1
I keep a Brompton six-speed folder in the back of my Grumman AA5 most of the time, and if I need to use the bike at home it also handily straps onto the back of my motorbike. But with the AA5 folding back seats and sliding canopy, a full-size bike drops in easily.
I’ve put a normal (non folding) full size road bicycle into the back of a Cessna 172 without removing the rear seats. Both wheels had to come off (the bike has quick release wheels) and an old sheet/tarp/etc. is required for the frame to stop the oily bits from making things dirty.
