Hi Lewy,
Now here is a legal technicality for you. Legally you don't need L plates for your test. The L plates are a condition of your provisional licence entitlement but as the examiner is not an instructor and is not supervising the rider during a test the normal licence conditions don't actually apply. It's the same in a car. The examiner is not 'supervising' the driver as required in normal driving conditions.
So if the driver crashes or commits an offence during the test no legal onus falls on the examiner as they are not supervising for the purposes of the provisional licence conditions. (Just talking about the actual driving licence regs here - not any duty of care etc)
It is the one time a person can drive (or ride a big bike) without being supervised, i.e. 'accompanied' in the legal sense, by a full licence holder.
It is a DSA requirement. (I had to display L plates when I was doing my car instructing tests - what's that all about)!!
Just a useless piece of information..... a good pub quiz question may be.