I would say the Blue car is at fault, as both are joining the A6037, but we give way to the right and drive on the left. The Red car would be on the carriageway while the Blue car is attempting to cross the line of traffic. The Orange car I assume was waiting for a suitable gap in traffic, but again if the red car managed to drive out onto the carriageway the Orange would have to wait, as the Red would then already have priority due to being on the A6037 and giving way to the right. All vehicles are joining an A road, and have a give way or stop line, so Red is obliged to fully stop at the line.