From a simple google search, it is 5yrs after conviction (innocent until proven guilty) until a Drink Drive conviction is spent.
Points remain on a licence for 11yrs, but it is unlawful and discriminatory for those points to be used to decline, cancel or increase the premium of a drivers insurance, as the conviction is spent after 5yrs. The Financial Ombudsman has ruled on this.
So that's the legal standing.
With regards to recruitment, if it's unspent, you have to declare it on the application form. Failure to do so, and it coming out at a later date, even years down the line, will most certainly be met with gross misconduct- dismissal. A serious breach of trust, failure to disclose material facts by ommission.
If it is disclosed, the TOC will weigh up your application against all the others, but, realistically, such a serious, recent conviction is a liability and most TOCs aren't going to risk spending thousands on training you. If all the applications are equal, a Drink Drive conviction will count against you. When you're competing against thousands of other applicants...