Pull over and check the wheels. Chances are that they are out of balance because a rim weight has come off. Then drive at less than 70 to a garage or tyre place to sort it out.
I wouldn't advise slamming on brakes and swerving. Just ease off and if the juddering stops its most likely the front wheels need balancing, though it could also be loose wheel nuts or worn bearings.
Slow down and return to the inside lane when it's safe to do so.
If the juddering stops, continue to the next exit and get the wheel balance, steering joints, tyre pressures checked etc. as soon as possible.
If the car is starting to judder, as above, but it could be a mis-fire on the engine, running out of fuel, blocked fuel line, injector, spark plug etc.
Why would he be in the outside lane doing only 70?
Why, sticking to the speed limit whilst overtaking a lorry, restricted to 56mph, in the middle lane whilst overtaking another lorry on the inside lane, also restricted to 56mph.
Crazy init?