The prize was won in December 2013. The claim deadline was 11:00 on Monday, June 16, 2014.
A National Lottery spokesperson said: "We tried very hard to find the ticket-holder and it's a real shame that they have missed out, but there is still one winner —the nation. This money, and all the interest earned over the 180 days, will now go to benefit projects all over the UK funded by The National Lottery."