you have to insure at current market value as mentioned in the renewal notice which I received last week. it says
It is in your interest to revise the estimate value for which you wish to get insurance cover for your vehicle so that it corresponds to its current market value, otherwise in the event of claim the Company's liability for loss / damage to the vehicle will reduce proportionately.
considering above statement, in previous year when car was insured at lower than market value, my friend have to pay extra amount as "under market value insurance charges" along with depreciation ratio at time of claim.
so its best to insure at Current Market Value