The conviction for drink-driving is now almost certainly 'spent'.
If your friend was only disqualified from driving (i.e. if there was no fine imposed as well) then the conviction became spent at the end of the period of disqualification. If a fine was also imposed the conviction became spent 5 years after the date of the conviction (assuming that the ban wasn't for more than 5 years - which is very unlikely).
Only if your friend was imprisoned for the offence will it currently remain unspent. (For a prison sentence of less than 6 months the conviction would become spent 7 years after conviction. If a prison sentence of 6 months or greater - but less than 2 years 6 months - was imposed it would take 10 years for the conviction to become spent).
Assuming that the conviction is now spent, when your friend is asked whether he has any criminal convictions he can now legally answer 'No'. The only exception to this is when the type of employment is exempted from the Rehabilitation of Offenders Act. (This would apply to jobs with Health Authorities, in schools, etc. The fact that an exemption applies would be made clear on any application form).
http://www.lawontheweb.co.uk/rehabact.htm
Chris