Also forgot to say that should you have 2 policies on your car in place at the same time and have a claim; being the sh!its that most insurance companies are, each will tell you to claim off the other.
So it�s not to be recommended.
If however you want to change insurance companies because of a change of circumstance (e.g you have moved � and your insurance company wants to sting you), you should come to an agreement with your current insurer on the period of cover they will offer, based on the amount you have paid to date � and arrange alternative cover from when that cover ends.
The above happened to me the last time I moved house, my then insurer doubled the premium for my new address, although the post code area was no worse an insurance risk than my old address. Just another way of insurance companies ripping you off