Whoever you paid your premium to. Look at your bank statements and ask your bank if necessary. Look at your emails from around the time. Look at your papers- it's always a good idea to keep a copy of your policy in your glove box. If you can't remember any of teh circumstances -eg did you go on a comparison website, did you jsut renew your existing cover, etc- then maybe you don't have any insurance.
You can also go on Experian and look at your credit file as they may have done a credit search
As furrypusscat points out, your certificate of insurance will state the insurer, even if it was issued by an intermediary such as an insurance broker. There is another insurer behind the stated insurer and that organisation is called an underwriter - if their name is not in the documentation (as I would expect it to be) then the insurer will tell you who they are if you ask for that information. However, your dealings will/should always be with the stated "insurer" alone. The underwriter acts basically as the insurer's insurer.
Then use this link, it is to check other people's cars if you need to find insurance details after an accident or other incident.
http://www.askmid.com/askmidenquiry.aspx
You will need to 'make up' some of the details , like why you need the information. But that link to MID gives the name of the insurer and the policy number!
Why do people keep asking this question? I don't have, nor need, a car so I don't know about car insurance. But I remember who my house insurance is with and who I used to use fro Cat Insurance (until the premium got silly).
Probably because so many of us insure our cars online now wolf63 and remember little of it. If my left depended on it I wouldn't know who mine was with and would have to wade back through my emails. Not proud of it and really should get more organised, but I am not resorting to buying a printer and ink. Have wasted far too much time and money on that and not doing it again.
If you download and install "cutepdfwriter" you can create a pdf instead of printing to paper (just select "pdfwriter" as your default printer). At the end of buying something, including insurance, it usually gives you the option to "Print this Page". Using cutepdfwriter it will ask you for a filename to save it to - you then have a permanent record of the transaction without needing to print and keep paper copies.
Good idea, I'll always be getting round to doing something like that ...... just need to fire up the laptop. Tell you what, lets all write these things down somewhere like the old days!
As well as my spreadsheets, email and download files I still keep some boxes/folders marked Insurance, Banking, Work,, Certificates etc- but I suppose the latter can get destroyed in a housefire
You can get fireproof safes for such documents ff - I think we paid about £100 for ours a few years ago, so not a fortune. We keep all our important certificates etc in it, as well as a hard disc with all my data backed up onto it.
It's worth thinking about because if your house does burn down you will lose all the information required to claim off your insurance (Policy no etc).