Section 210 of the Road Transport Act 2013 requires that if a person is convicted of a Mandatory Interlock Offence the court must either make a Mandatory Interlock Order OR a Interlock Exemption Order. There is no discretion given to the court.
A Mandatory Interlock Offence is one of a set of prescribed driving offences and are set out in Section 209 of the Act. The statutory rules detailing the offences are quite complex and advice should be sought in relation to your particular circumstances. Broadly speaking if you are convicted of a drink driving offence a second time within 5 years the provisions are likely to be enlivened.