"A person drives dangerously when:
The way he drives falls far below what would be expected of a competent and careful driver
AND
It would be obvious to a competent and careful driver that driving in that way would be dangerous"
The definition of 'careless driving' is this:
". . . when the accused's driving falls below the standard expected of a reasonable, prudent and competent driver in all the circumstances of the case"
The wording of the statutary warning that is given is that the driver will be reported for the question to be considered of prosecuting him/her for the offence of dangerous, careless or inconsiderate driving.
The decision isn't made by the officer at the scene but by the accident investigation team in conjunction with the CPS. They will opt (unofficially) for the best hope they've got at court so that court time is reduced, rather than necessarily going for the full offence. If it does go to court it is unlikely to be for dangerous driving (if you've been given the full story).
From the circumstances described, it sounds more likely that he would be summonsed for be "not in proper control of the vehicle" or "careless driving" rather than dangerous driving.
Wait to see what comes through and then speak to a solicitor if necessary. As to waiting times, you could always try calling the local police station to get an update.