Have look at this company…
http://www.abbeygateinsure.com/
I have my work van insured with them. I found they were competitive, helpful, plus they sent me all my policy documents in both Spanish and English.
My parents have also insured their vehicle and their property with them.
Although I paid for my policy in one go, they do offer different options, including monthly.
Just a pointer, as with any insurance company, don’t be frightened to haggle a little. I mentioned that although my parents were customers of theirs, I still had a few “quotes” and that they would need to “sharpen their pencil” and give me a good price. They came back much cheaper than any of the quotes I already had, as well as my renewal price from Allianz, my previous insurer.