About Do not block the junction — even with priority: which statements are correct? (multiple answers possible)
If you have to let a priority vehicle (blue flashing light and two-tone horn) go first, you may move onto or stand on the junction when that is needed to make room.
Even a driver who wants to turn left on a priority road and waits for oncoming traffic must stay before the junction.
The rule applies to everyone entering the junction, even on a green light: if the far side is at a standstill, you keep the passage clear and wait before it.
If traffic beyond the junction is stuck, you may drive halfway onto the junction and wait there.
Explanation
Waiting even halfway onto the junction still blocks the crossing traffic — wait before it, not on it (Book p.103).