We'll never know.
This morning I was travelling own the slip road at 62 m.p.h. and there was a very congested lane one. There was what I perceived to be a safe gap in front of a HGV, so I built up speed to overtake moving vehicles and join. There were no visible safe gaps in my mirror behind the gap I took and with traffic to my rear, it would not be safe to slow down and wait for a gap.
As I joined, the last vehicle I had passed on the slip road (a HGV)
Was I wrong, was he or were we both?
I stand to be corrected, but the on-slip is separated from the main motorway carriageway by a dashed line, and therefore you have no right-of-way to join the carriageway: you should not force / slide / tailgate your way on. If that means stopping on the slip, then stop.
Stopping on the slip can leave you in a very prone and dangerous situation, when L1 is busy and fast flowing. You can have traffic tearing down the slip behind you and be faced with getting up to the speed of L1, from a standing start. The much safer option for all, is often to squeeze into a less than adequate space.
Sorry to sound dense but I may have got myself a bit confused. Was the HGV you joined in front of, the same one you saw having the gap in front of it originally?
That was my concern. How could I then build up speed if I am - according to rule 259 - not travel on the hard shoulder. There are cameras around there and what if I was picked up and fined? I've been fined for moving through a red to let am Ambulance through which was penned in by cars behind me!
That is the official and correct answer, but this is the real world....
It can be safer if you're dealing with a BMW or Audi driver. You know that if you give them a flash, they take any opportunity, then they're gone, sorted.
If they're in a Japanese/Eurobox, they WILL p*ss you about.
HGV travel at around 58-60 maximum, (if their governors are set correctly), so the OP driving at 62 should not have been in danger of being hit. Dropping a vehicles speed by 2-3mph to allow someone in safely is not going to be much of a detriment to your overall rate of travel in the grand scheme of things.