I have always felt that regardless of RoW issues,"The Duty of Care" in the slip road scenario rests primarrily with the driver with the best view, IE the one in L1!
Under Maritime law, there are rules about who should give way to who But, *everybody* still has a "duty of care" to avoid collisions! (That would be my *mod* for the Highway code!)
IE if somebody who has "Right of Way" Ploughs on regardless because they think they are entitled to do so in a manner that results in an accedent they can neverthless be found (RoW not withstanding) liable for the consequences!
Drivers in slip roads frequently have "Rotton" visability of what is going on on the main road. and It is not always possible to accelerate to the "56 MPH" that HGV's insist on in the distance provided (I can manage, in my van, 45 tops on a typical slip road! I will aim for a *gap* in L1 but this will typically require the guy behind to slow down or change lane
THERE IS NO OTHER WAY!)
(In my car, this is a diferent issue. I believe strongly in the "Emergancy start" stratagy IE I accelerate hard and *brake* to enter the traffic stream! It
never fails!

, But then the Rover Vitesse has *four times* the power and *half* the weight!)