It would appear that if you declare yourself as a �finder� then the NL will search for any valid holders or investigate any claims from people who claim to have lost the winning ticket.
Assuming they haven�t written their n&a on the back, then should the actual purchaser not materialise then, at their discretion, the NL will pay the winnings to the finder.
It would take a cool calm devious head to claim a jackpot prize on a found ticket without declaring it �found�, and then if found out you run the risk of not getting the money as it would be seen as being �stolen�. If not, jackpot.
http://www.national-lottery.co.uk/player/infor mation.do?info=playlottorules
Section M refers.