The odd thing here is that I don't think that's a UK road sign. Without the diagonal, and with the RH car in red (appears white on the car's monochrome display) it would mean "No overtaking". So logically a similar sign with a diagonal through it would denote the end of the no-overtaking zone. But I don't think we have such a sign in the UK, although other countries might. I suspect this is something loaded in the car's traffic sign database for other countries, and it really shouldn't appear on a UK car. But it does (I've seen it as well) and it's not clear what the camera has picked up.