Just happened to spot this thread when looking up something else, so sorry for the dredge, however I felt it prudent to reply.
Anyone in the UK can buy a Night Vision weapon scope without a gun licence, the only issue is if you buy it and intend to remove it from the country.
Night Vision Weapon sights with image intensifiers are prohibited for export, even to neighbouring countries such as France and Ireland for example, unless you have an Export Licence to accompany the goods.
The Pulsar Digisight does NOT have an image intensifier, however as it is a weapon scope with a magnification greater than 4x, the same rules apply, an export licence is required in order to remove it from the country, used, new or otherwise. If the dealer you buy it from is aware that you intend to remove it from the country he/she is also breaking the law in supplying you.
The same applies believe it or not to a 6x42 £29.99 airgun scope, this is also prohibited for export as it falls under the same classification.
You can find out more here
http://www.bis.gov.uk/assets/biscore/eco/docs/control-lists/12-750-uk-military-list
And rating ML1D and ML15 applies to what we are discussing
Thanks for reading
Paul