You would expect third-party cover to be the cheapest because it is the lesser cover, just covering the person you bump into and their car. Yet don’t expect car insurance to be logical.
With some insurers the mere fact you have selected comprehensive, which includes your car too as well as fire and theft, means you’ll be assessed as a lower risk (based on actuarial history, which is what an insurer will hold about a particular age group or address, for example, on which they base their premiums).
This can outweigh the fact you get more cover, and make your policy cheaper.
There are no hard rules here, it’s a matter of trial and error, yet if you’re just looking for the very cheapest cover, never only check third party.
My auto renew quote was £210 for 3rd party only. I went to a comparison site and got comprehensive breakdown cover & free car hire with the same company for £40 less.Forumite DobbieSloan