Thanks for your replies. I agree that it seems a badly designed junction and is 'an accident waiting to happen'.
The reason that I asked the question is because my niece has just failed her driving test for the second time at that junction. It is at the end of the road from the test centre in Leighton Buzzard so examiners tend to take the test drive out that way. My niece had gone out that way many times with her instructor who had told her that she should use method B. This would allow drivers turning off the main road to proceed without being held up by her vehicle. My niece queried the advice, saying that there were no signs or road markings to suggest that, it was counter-intuitive, and her car and cars turning the other way would block each other's view of oncoming traffic.
@Brandane gives the most obvious reason why B is wrong - because long vehicles couldn't go that way. It is clearly wrong that some vehicles should use one approach and others the alternative.
My niece took to driving very easily. She was very upset to fail the first test. She got only 2 minors. Her 1 major was that she was said to have incorrectly positioned her car on the right turn. She used method B, as taught by her instructor. Wrong! She should have used method A... She told the examiner that she had been taught B. No, no, no - it has to be A!
So, another test booked. Test #2 was with a different examiner. Out by the same junction using the correct method, A. My niece was confident that she had passed. Result - no minors, but failed on one major - incorrect positioning at junction. She should have used method B!!!
When told about the previous test, examiner #2 simply told her that it didn't matter what other examiners said. He was failing her and that was all that mattered.
It appears that there is a serious problem with driving tests in Leighton Buzzard. The test drive will usually go out by that junction. If you guess which way to position your car, you will guess wrong. If you ask the examiner which method they prefer, undoubtably they would see that as a sign that you didn't know what you were doing!
My niece refuses to take another test there, so is considering booking a further test somewhere else.
What a damn farce!