There a few angles to consider here :
Your existing earned NCD will be maintained, usually for up to two years after it was last used.
The NCD you are earning at the moment with your current insurer is unlikely to be rolled on one year if you are off the road for more than 3 - 4 months. This is not an issue however if you have already accrued a full NCD.
Don't foget to advise your current insurer that you wish to suspend cover ( you will need to return your cert ) . If you suspend for greater than one month you should receive a refund as Third party cover would not be in force.
Hope this helps.