I have just had same problem today. Went to renew with tesco, again another increase, even though no claims made ever, Full no claims bonus... I came on moneysupermarket.com and got a quote for less than half renew quote, and with a courtesy car. I phone back Tesco, and they start offering me all sorts to stay with them - I said no, because they should offer all this stuff to loyal customers. If you have a "bargaining tool" such as a better quote, you can get all sorts of benefits. So I have learnt a lesson to never renew with same comany again. always look for better quotes !!!
I have written to tesco to ask for compensation for years of wasted money by renewing with them without shopping around. Excess is higher though, but I don't mind this !!!