I asked my own insurer who don't do it but pointed out that for the first year, if the car was a write off, they would give me the full purchase price back so the cost of the gap insurance should be considered over two years and not three
No differences in rates of tax ( IPT ), supplier prices and volume means that you can buy on line from specialist brokers like https://gapinsurance123.co.uk/ or https://easygap.co.uk/ for a lot less. Which have just done an review on gap insurance it is worth looking at