Car insurers are very wary of insuring people with criminal convictions. There is a world of difference however between convictions that are 'spent', and those that are not.
Under the Rehabilitation of Offenders Act an offence may become spent after the passage of a certain number of years from the end of the sentence. Just how long this is depends upon the sentence; and in the case of imprisonment for more than four years, it lasts for the offender's lifetime.
Once an offence is spent it does not have to be declared to most employers - not all, since some jobs are more sensitive than others - or insurance companies. Unfortunately some companies do not observe the spirit of the law.
Officially it is illegal for an insurer to discriminate against any person on the basis of a spent conviction. However there are some insurers that insist that anyone who applies for a policy must inform them of any non-motoring offences that they have ever committed. This is of very dubious legality indeed, because insurers must follow data protection legislation in the same way as the rest of us, but it happens.
Bizarrely, research has suggested that people who have had prior criminal convictions actually make fewer claims than those who have not – so discrimination against ex-offenders can be counter-productive for the insurance companies.
If, on the other hand, an offence remains unspent then the insurers are well within their rights to either refused to provide a policy, or to increase the premium, perhaps considerably.
Every car insurance proposal form will include a question about unspent convictions and it is vital that this question is answered honestly, since failure to do so can constitute fraud and could nullify the insurance policy completely. However you are not obliged to mention spent convictions. This is not usually made clear by the insurers however.
You can get more information about the Rehabilitin of Offenders Act, and about how long it takes for an offence to become spent, from the NACRO website.
In the meanwhile there are still a lot of more enlightened insurers who are perfectly happy to consider applications from people with unspent convictions. However this is a very specialist area and you will almost certainly need the help of an experienced broker.