am I likely to get nicked

[Red Herring]

Wow, isn't it easy to get some people going, although I do accept it was a little provocative. There are two types of fixed penalty tickets dished out for VEL (That's Vehicle Excise Licence) offences. The £60 ones are for persons who have no tax on their vehicle, and they are the ones you see the most. Favorite amongst ANPR officers but now in general circulation they should only be given out if the vehicle is not taxed.
The others are £30 tickets. They are for the offence of "failing to display" and should be given to the driver/rider who has tax, but just hasn't displayed it. Technically if the tax is in your pocket, on the offside of the vehicle, or in the case of a motorcycle behind the rider (I kid you not) then you could be given one, but it takes a really anal kind of traffic officer to even know they can let alone actually write one out (I can say that, I'm not on Traffic anymore).