There would be no evidence to offer to support a charge of excess alcohol and guilt of that offence cannot be assumed by the magistrates. However, as jake says, refusing to provide an evidential specimen is offence by itself.
Disqualification (12 months minimum) is mandatory and magistrates' sentencing guidelines for the offence suggest a ban of 24 months. In addition the offence carries a maximum of 6 months imprisonment, but the guidelines suggest a starting point of a community penalty.
The fact that an accident occurred will aggravate the offence and may lead the Bench to impose a higher penalty than their guideline starting point.