they only have type approval to cover one lane per camera,
just switch lanes when you go past one and back again and so on, hey presto no speeding offence!
Generally you will be breaking the law on two counts if you change lanes.... The cameras I have passed are in areas which prohibit changing lanes with signage and road markings indicating as such. If you change lane you are breaking that law. If you change lanes with the intent to pervert the course of justice that is another offence.
They work by offsetting your time by number plate recognition, so I suspect that they will be able to pull out a long list of registration plate that go in one end and are not picked up by that camers at the other.
Those type of cameras used on normal dual carriage (I am not aware of any) you would not catch you if you changed lane.