Theoretically, you're allowed to import an unlimited quantity of 'duty paid' (rather than 'duty free') cigarettes from any EU country (with the exception of a few new member states), as long as they're for your personal use. ('Personal use' includes bona fide gifts to others but not cigarettes that you'll resell, irrespective of whether they're sold for a profit or not).
HMRC have a guideline figure of 3200 cigarettes per adult as the maximum they'll accept before challenging travellers about whether they're really for personal use. However, it's important to note that HMRC could still seize smaller quantities if they had reason to suspect that they weren't for personal use. In particular, if you bring back several different brands you risk having all your cigarettes confiscated because it's unlikely that HMRC would accept that they were all for personal use
Chris