I will give you another real situation, not the same, but kind of similar.
A few years ago in 30mph street near me a child on the pavement, to use the mother's words, 'slipped my hand',
The little lad dashed between two parked cars and was killed by a moving car.
Witnesses said the driver was doing about the speed limit, but had no chance of avoiding the collision.
The driver was not charged.
Perhaps you all think he should have been, but I do not.
Thus it is possible to collide with something in front of you while still being a careful and competent driver.
No one is suggesting Mr Mason dashed into the path of the car, apart from anything else he was riding a bicycle.
But the car did not deviate - that's on the CCTV.
Mr Mason must have deviated or he would not have been hit.
How long was Mr Mason in front of the car before he was hit?
Again, no one knows.
But the collision investigators seem to have concluded it was not very long, maybe a second or two.
If that is so, a careful and competent driver had no realistic prospect of avoiding a collision, given reaction times and stopping distances.
Thus the careless driving part of the charge is a non-starter.
For the private prosecution to have any chance of success, the family will need to come up with new evidence, hopefully that Mr Mason was cycling in the path of the car for several seconds before he was hit.
Evidence of the driver not wearing glasses would also do, clearly a careful and competent glasses wearing driver would not drive without them.
Without new evidence, I think the DPP will take the case over and stop it.
Even if the case proceeds to a crown court trial, a defence barrister will make mincemeat of it.
As
@spen666 posted earlier, a defence application at the close of the prosecution case that there is no case to answer looks very likely to succeed, assuming the judge doesn't chuck it earlier.
@Arrowfoot tells me he can 'guarantee' the prosecution case will proceed, perhaps he/she knows something I do not.
I'm not bold enough to guarantee anything with the law, but I can't see how, as the law and the case currently stands, there will be a conviction.