If you're overtaking a vehicle yourself, it would be impossible for anyone to overtake you on the inside.
It would be impossible for anyone to SAFELY overtake you on the inside.
Don't be a fool and break the two second rule - two chevrons and all that jazz gives plenty of room for an idiot to dive up the inside lane and cut back across again. You seem to be working under the pretense that someone should drive RIGHT up to the back of a lorry leaving no room whatsoever - pull out accelerate past - and pull straight back in again leaving room for little more than a fag paper between his bumper and yours.
Sensible, carefull driving would involve pulling out to overtake in plenty of time, certainly two chevrons / two driving seconds behind the vehicle, and not pulling in again until you can see the entire front of the vehicle in your wing mirror. If the next lorry is two seconds ahead ( or the time to reach it is less than 30 seconds, the suggested maximum 'dwell' time in the outside lane ) then you shouldn't be swerving back between the two vehicles only to pull back out again 5 seconds later. However - that sensibility leaves room - room that morons like to use in driving dangerously.
Sensible, careful driving leaves room for unforeseen incidents. Moronic undertakers see that room and think ' I can endanger my life, the life of other motorists, break the law AND shave as much as a minute from my journey if I dive through there'