informing insurance over a no fault no damage accident?

[chaosagain]

My MIL was driving at about 20 mph in a busy London 30 zone. A boy ran out in front of her car with no warning. Traffic was moving, this was not at a crossing etc. She hit the poor lad who got back up and limped/ran off. She ran after him to make sure he was ok and get him to sit down while she called an ambulance.
Long and short of it: he was taken to hospital to check on his foot but paramedics thought he was ok, thankfully. Police took a statement from MIL under caution. Bus driver (next to MILs car at time) gave her their reg and CCTV number as thought it might have been caught on bus CCTV and could corroborate what happened.
Police gave MIL a crime ref number. When she asked if she should inform her insurance the police officer suggested not to as it would only increase her premiums and there was no damage evident to car. She's worried that she's supposed to.
Is there a legal requirement to inform the insurer?

Do not inform your insurance company.

Place marking. Not sure that the police officer gave her good advice. You're absolutely right to investigate the implications of not informing your insurers.

I am fairly sure (someone will come on who works in the industry and can confirm this) that insurance companies have quite individual rules about what they want to be told about, and what they don't. Can you bear to sit down and read thruogh the small print of her policy?