Tree goes for a drink...That’s exactly why Brits drive on the left.
In the Middle Ages you never knew who you were going to meet when travelling. Most people are right-handed, so if a stranger passed by on the right of you, your right hand would be free to use your sword if required. (Similarly, medieval castle staircases spiral in a clockwise direction going upwards, so the defending soldiers would be able to stab down around the twist but those attacking (going up the stairs) would not.)
https://www.historic-uk.com/CultureUK/Why-do-the-British-drive-on-the-left/