I understand what Dante meant about being "all over the track". It's your rhyme structure, you seem to be flowing all over it. You're not on beat, so to speak. You need to flow with the beat, start at the begining of the bar. (I'm not an expert though, so I could be wrong)
Americans can't understand the British London accent, and they hate it, so you'll always get that from anyone over the water. The same reason why so many UK rappers are failures in the US. Plus I tend to think most UK rappers aren't as good with the English Language, odd as it seems.
Anyway, it needs a bit of work, take the criticism on board and work with it. You'll have to be pretty damn good to get praise from a US hip-hop fan, they're spoilt with all their good artists. You may do better getting feedback from people from the London scene. Grime and garage fans (which is pretty much UK hip-hop) are more forgiving. Plus they'll understand the accent better.