This might be worth a read.
https://www.moneysavingexpert.com/in...ome-insurance/
One renewal quote I had recently was with M&S (as you, also +35% on last year). I searched online (comparison sites and those not on comparison sites) and found comparable cover at less than half the price (i.e. 30% less than last year). Definitely shop around, and do it in good time (3-4 weeks before your renewal date). [I ended up going with SwiftCover - good Defaqto rating and good online reviews.]