Part of the problem could be the part of London you are living in; if your borough/postcode has a high incidence of motor vehicle crime that could load the premium.
I always bite the bullet and sit by the phone for an hour or two and talk to companies direct, I simply don't believe the comparison sites.
Whilst not doubting what Kristal says about her experience, my own experience of Saga (and that of some others I have asked) is that they are relatively expensive compared to average and they over-rely on their 'over 50s' badge to try and sell to people who are generally less inclined to shop around. That is why they are able to report that 'X made a saving of megabucks by swapping to us'.
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swinton quoted me 285 renewal on house insurance -got it for 138 from Saga. Swinton quoted me 450 renewal on a nissan micra and we live in a rural area good postcode -got it at Saga for 320. Disagree with the fact over 50's are less likely to shop around - thats ageist! ;-)
I've been with LV for a few years now. Last year my premium "increased" to £214.00 for Fully Comp on a Renault Scenic 1.6. Renewal due in April, I await with anticipation.
Quite a few insurance companies now seem to be moving to automatic renewal (if you don't ring them) and increasing the premium over the odds in the hope that you can't be bothered to ring and cancel.
If you can find a cheaper competitor on line then ring and tell the original insurer and they'll soon lower the price to keep you.
Incidentally, I use L.V. also.