I was in the middle lane to allow joining traffic from junction 4 to merge onto the motorway. The car in front pulled out to overtake a slower moving vehicle in front and I followed. The offending vehicle (YG21DGF) was approaching from behind in the outside lane but was a safe distance away at this point. I hadn't realised how fast he was travelling until he was in my rear view and much closer. He then pulled into the middle lane as the motorway was returning back to 2 lanes from 3. The car in front had merged back into the middle lane & I indicated to do the same and starting to move into that lane when the honda sped up and pulled alongside me which blocked my way. I had to swerve to avoid hitting him as he held his line and seemed intent on getting past me. I sounded my horn on the very minor chance that he hadn't noticed me (I saw that he was wearing sunglasses even though it wasn't particularly sunny) but he continued to hold his line and moved past me in the middle lane. After I sounded my horn and dropped back behind him, I made a hand gesture and then he slammed on his brakes and continued to speed up and slow down until I pulled into the inside lane to exit the motorway at junction 3. When I changed lanes he pulled into the inside lane at the last minute, in front of me. My intention was to exit the motorway but it seemed as though he thought I was as reckless a driver as him and was possibly trying to undertake his vehicle. As I left the motorway I glanced over at him to show my displeasure and he also looked over towards me and appeared to be muttering something.
Approx mid 40's with short, neat, black hair. Mixed race male. Wearing sunglasses so couldn't distinguish any facial features or eye colour. Appeared to be tall judging from his seat position.
