Definately illegal, but the odds of getting caught are slim.


As per RickyLee's suggestion though, adding your mum as a named driver in case she wants to drive the car when you are a youngster will bring your insurance down, I found this out by accident when I was a teenager and borrowed my mums car for the weekend and added her to my insurance just in case she needed to use mine, when I found out how much extra it would be to add her, they sent me a cheque for a partial refund.
Thats perfectly legal as his mum only needs to take the car down the shops once during the year for her to need to be insured on it, so no chance of them proving any sort of scam going on here.
Doesnt make the same savings that the sort of blatant insurance fraud you are talking about does though of course.