I assume that as it's only 3 points, it's probably just an SP30.
if that's the case, then so long as you don't have previous claims or convictions that are disclosed, it's unlikely to make a massive amount of difference (if any).
We don't take that much notice of a single convictions such as this (it's not to say you shouldn't disclose it as each case is taken on it's own merits), but if it's anything other than a speeding conviction, there could be an increase in premium.
Generally, the only single convictions that make that much a difference, and could potentially result i nyour policy being voided from inception are:
No insurance, drink or drugs related, driving whilst banned, and failing to provide the driver's details (MS90).
They are all generally automatic voids.
Most insurers will also ask for convictions within the last 5 years, and claims within the last 3 years. The licence mandate (which we always use and have a very good detection rate of undisclsoed convictions off) will show all your convictions over the last 5 years, so I hope that's the only one.