Did you receive a fine as well?
If you weren't fined - it was spent 9 months after conviction.
If you were fined - it is spent 5 years after conviction.
"Disqualifications
The rehabilitation period for a disqualification is the length of the disqualification. If a person is disqualified at the same time as receiving another penalty, the longer rehabilitation period applies. (For example, if a motorist is banned from driving for seven years and fined - which takes five years to become spent - the rehabilitation period would be seven years, not five years.)"
http://www.lawontheweb.co.uk/rehabact.htm