No need to be condescending mate, I know the difference between a stop and a give way.
But if you don't merge in properly and instead "give way" then you end up stopping because the entrance is so short that by the time you are going 100k and giving way then you end up off the road, which is why people in the end are going 20k's under and merge on which defeats the purpose of it all.
Sounds like you just described exactly what darkplague has done - got up to speed and "slot" in a gap.
I just think it's stupid how the law is that they don't have to let you in, coz that leaves three options if someone isn't courteous:
1. Slow down until someone else lets you in or there is a gap (which 90% of the time you end up having to stop, which is what I meant by stopping while giving way.)
2. Stay up to speed and do 100k along the side of the road hoping for a gap even though the merge lane has ended haha.
or
3. Make your way in ("barge" so to speak).
Fair enough it's different for every circumstance, but this one sounds like the cop was just being a douche.
But yeah there's noway you'll win in court, if everyone was courteous (including the copper), then it would all be fine
Anyway the question has been answered though, and unfortunately it's illegal.