You can only pass on the left when:
There are two or more lanes on your side of the centre line and you are able to pass safely by using the left-hand lane
The reason I don't know if it is the actual law is because the road code also says:
Remember, it is against the law to cross over a no-passing line on your side of the centre line to pass another vehicle.
I don't even know if the two-second rule is a recommendation or the actual law.
You say you have 2 witnesses and the other driver has none? How can this be? If the witnesses saw you hit the other car then those witnesses can be both your witnesses and the others car driver's witnesses couldn't they?
If the other driver did speed up and go over the speed limit then it is going to be difficult to prove if there is no speed camera that caught it or no tyre marks left by skidding.