Whilst the value of your car is depreciating, the important factor for the insurance company is the value of any car you may hit, the injuries you may cause and so on.
In today's climate, the likelihood of a personal injury claim is higher than ever, mainly due to these 'no win no fee' accident claim handlers that advertise everywhere.
So while your car may be of little value, a collision caused by you could literally cost your insurance company hundreds of thousands of pounds.