I got some from http://www.likeabike.co.uk/likeabike_spares/likeabike_hand_grips.php

IIRC the law was going to be up to 150cm tall to use a booster seat, but it was then decided that wasn’t practical.

So it isn’t the law for your daughter to use a booster seat, but you are not doing any harm as long as the seat belt is positioned correctly over her shoulder and her head isn’t too high above the top of the seat.

I win! My littlest boy has been doing the school run on a pedal bike (no stabilisers) since he was 22 Months!

Before that he did it from about 19 months on his Puky.