The length of time it takes for a conviction for drink-driving to become 'spent' depends upon the sentence imposed by the court.
If only a driving ban is imposed, the conviction is spent as soon as the ban is over. If a fine is also imposed, the conviction becomes spent at the end of the ban or 5 years after the date of the conviction, whichever is later. If a prison sentence (not exceeding 6 months) is imposed, the conviction becomes spent 7 years after the date of the conviction (unless there's still a ban in place). For longer prison sentences, not exceeding 2 years 6 months, the conviction becomes spent after 10 years.
The foregoing text assumes that the person is not convicted of any other criminal offence before the original conviction is spent. (If so, the conviction for drink-driving wouldn't be spent until the other conviction is as well).
Once a conviction is 'spent', there is no need to declare it when applying for insurance, or for most types of employment. However, employment with children and vulnerable adults is exempted (as are jobs such as the police); convictions are never spent when applying for these jobs.
Employers can normally only obtain CRB checks in relation to applications for those types of jobs where convictions never become spent. Any CRB check will always show all criminal convictions, including those which (for most purposes) are regarded as spent.
http://www.lawontheweb.co.uk/rehabact.htm
Chris