Your driving examiner will ask you to read the number plate on a stationary vehicle before you start the practical test. The distance requirement for the eyesight test using old style number plates is 20.5 metres or 20 metres if the new-style number plate is used.

If you can only read a number plate when wearing glasses for the eyesight test, by law you must wear them whenever you are driving, including the test.
 
New-style number plates are easily identifiable starting with two letters and a number eg., GU 11 KRR..