What applies at junction with a stop sign if the stop line is covered by snow?

When you have a duty to stop, you must stop completely and give way. You should stop at the stop line or, as in this case, if the line is covered by snow, just before, but not on, the intersecting road – where you can be clearly seen and have a clear view.

You may only proceed when you can do so without endangering or obstructing other road users.