Collective redundancy consultations do not apply if you are proposing to make less than 20 people redundant.
If you are planning on making between 20 and 99 employees redundant the minimum consultation period is 30 days and, if more than 100 employees are at risk then the consultation period is a minimum of 45 days before the first dismissal can take effect. This has recently changed and, before 6 April 2013, was 90 days for 100 or more employees under threat of redundancy.