Hey Skywards,
I don't know about the UK. But every opticien I went to couldn't complete it either. Nobody had the right equipment.
I would advise you to look up a special eye center.. Or the hospital (that is where I tested my eyes (they filled in the whole form).
Be sure to do it as soon as possible! When I called the eye center in august (a special kind of place that focusses on (geuss what) eyes..) they said the first possible date was 15 november.. So do it fast!
Hope you find this usefull!