I can't think of any 8-sided signs - unless it is two square notiices on the same pole. I've googled the Highway Code and there are no octagonal signs! Road could be another 4-letter word.
At the junction you will find a red octagonal sign with a white border with the word "STOP" written in it, where you must stop your vehicle behind the solid white line and wait until the road ahead is clear or has a sufficient gap for you to file into.
Stop and give way it was.