You have to take an eyesight test before you start practical test.
In good daylight you should be able to read a vehicle number plate with letters 79,4 mm (3,1 inches) high at a minimum distance of 20 meters (about 67 feet).
If you need glasses or contact lences to read the number plate, that's fine. You must wear them while driving.
At the start of your practical driving test you have to correctly read a number plate on a parked vehicle.
If you can’t, you’ll fail your driving test and the test won’t continue. DVLA will be told and your licence will be revoked.
When you reapply for your driving licence, DVLA will ask you to have an eyesight test with DVSA. This will be at a driving test centre. If you’re successful, you’ll still have to pass the DVSA standard eyesight test at your next practical driving test.
Crown Copyright. The content have been sourced from the 2019 edition of The Official Highway Code, and reproduced under the terms of the Open Government Licence.