Unnecessary use of sound or light signals is prohibited by traffic rules. Flashing your lights to signal that you wish to get past is considered unnecessary.

Driving too close to another car is illegal – and very risky. Driving too close to a lorry is even worse, as you are probably not able to see anything besides the lorry in front of you (and the lorry driver probably can't see you at all).

It is dangerous to blindly trust other people's assessments of what is safe; you should always personally make sure that overtaking is safe before starting to overtake.