Do you know the age of the bike that you can display black and white number plates on? I thought it was pre 1972 but have seen a few recently thatare a a lot newer than that. Here is one for example, 1981?http://www.ebay.co.uk/itm/122758633480?ul_noapp=true Has it become a rolling date or is it still fixed? Does anyone bother at MOT time? Do the Police notice?
I think you will find it has now moved onto a rolling 40 years as MOTs will next year (call me a cynic but I’m sure the b’stards are up to no good and the insurance companies will be wanting their bit)
I believe it is a fixed date, I think that many people like them on later bikes to perhaps enhance the classic look. At MOT it maybe depends on your relationship with the tester (I have to sleep with mine), and you’d probably be unlikely to both encounter a rozzer out on the street these days, and for them to notice or care enough to actually pull you.
The B/W (legitimately) plate on my Piecrust racer is both side mount and mounted on its side. That required an extra ‘favour’ at MOT time.
Plenty of info on the DVLA site .
I think that’s right. I wanted to get one for my 1978 Spada in preparation, but a supplier at Stafford Show said she couldn’t make me one until January. That said, a colleague has one on a 1981 Yamaha, and it was MOT’d no problem
I have a b/w display plate on my 1976 bike. Looks in keeping with the bike and is legible. Bought it online for about £5.
Not had any problems with the police. I suspect that it depends on the individual bike, rider and officer. For the MoT I have a regulation plate. My tester is a pal of Guy Wain’s; common sense approach and a Guzzi fan. No point in provoking a good bloke.
I have no interest in the ‘increased visibility from yellow plates’ argument which has been suggested by some observers. That’s another thread 'though 
Have fun
Steve
Thanks Al, as I read it, it is only pre 1973 vehicles, or if over 40 years old you have to apply to the DVLA and it must be a historic vehicle, otherwise £1000 fine.
Here’s what the DVLA says:
Traditional number plates for vehicles made before 1 January 1973 Vehicles made before 1 January 1973 may display traditional ’black and white’ number plates (for example, white, silver or grey characters on a black plate).
Since April 2016 vehicles manufactured before 1 January 1976 can display the older style plates. You must: (a) have applied to DVLA, and (b) be registered within the ‘historic vehicles’ tax class.
Vehicles constructed 40 or more years ago are exempt from tax. The 40 year exemption date rolls forward automatically each year on 1 April.
Simples!
Although my 850GT was registered in 1972, it has a yellow plate on the back. I seem to remember when they first came out, people wanted them as they were new and attractive. It looks like it’s probably original so I’ve left it on.
Also has a front plate, but fixed across the front of the fairing.
The way to get around it in London is just not have a number plate like many of the ped boys out there.
The police don’t do anything, see them everyday.
And there’s me worried about my plate being 1/2 inch under regulation size.
Mind you now my 76 le mans is a registered classic it’ll be getting a black number plate…
No doubt the insurance companies would view a black and white plate on a post '73 bike as an illegal mod and refuse to pay out on a claim. They’ll use any excuse they can. Sorry for the doom and gloom 
Yer rught tho Jez I reckon…these days however there aint that many coppers about that can be bothered…too busy…