Police don’t routinely ask for proof the nominated driver was insured unless you give them reason to doubt it.
You had a duty to ensure the driver was insured either via your insurance or by seeing a copy of their own insurance that gave cover when using other vehicles.
If you name your friend, they live in this country and promptly reply to their own S172 nominating themselves and then take up the CoFP if issued the police are not going to enquire about insurance status.
If you accidentally let your friend drive without insurance then best reply promptly and ensure they do too.
