I did not say that Rule 129 only applied to the offside, but form the OPs explanation and the purpose of the post it is on the offside. Looking again at the map, and following the road's course, resulted in my writing post #7. Technically an offence was committed, but I still doubt, in this instance, that any observing police officer would have reacted unless a dangerous situation was caused. Believe it or not, there are traffic police would sometimes despair of the ineptness of some road markings.
Unless he or his passenger knew the road, neither would be likely to be aware that a "second chance" to pull over to the right existed further along the road.
Thank you everyone for the information.
Yes, you are right. We were in the left most lane (3 lane road), driving at around 27-28 MPH, and when we realized that we were in a wrong lane it was already very late. The white solid line on our right had already been started. My friend checked mirrors, no one was in his right lane so he moved to right lane. I was looking at the signs but I think i missed the one which was showing the left most lane would not go to the tunnel. My mistake! And only after looking at the road on Google Maps I realized had we continued on that lane we could have merged back to the road going towards the tunnel.
I still feel bad we shouldn't have done it! My friends think I am paranoid =D .. And I agree this road is very confusing. So many markings on the road, on the sign boards and many lanes merging and diverging in such a small space. I hope that he doesn't get the ticket or our Easter plan will be cancelled. He will not take out his car!
Actually you are wrong - the left most lane does indeed go into the tunnel. The lane markings are intended to stop people switching at the last minute. The two outer lanes merge into one through the tunnel. Lorries over 2.8 metres high must use the left lane. If you look at the white painted sign on the lane you were on, it says "TUNL ANY VEH"