who were you insured with at the time of the conviction? That company MUST give you a quotation. If not, write to the Chief Executive and thereafter if still no satisfaction, to the Insurance Ombudsman.
You are looking a ta loading being put on your quotation because of your conviction. that wil ldepend on the level of intoxication and the circumstances of the conviction. If slightly over the limit and not involved in an accident or any other driving charge, then the loading shoudl not be as high as if you were very much over the limit and had an accident.
Good luck.