Well,
Putting the same numbers on twice doubles your expected winnings while also doubling your outlay. The result is the same. The only thing that's affected is the jackpot, where your winnings become 2/n+1 instead of 1/n, where n is the number of winners. This is slightly less than doubling your return, so actually your expected winnings have gone down by a very small amount.
( flatfrog Staring vacantly into space, Tue 12 May 2009, 10:54, 2 replies)

I just realised
That I failed to take into account the possibility that there *are* no other claimants to the jackpot. In that case, you win the same amount as with one ticket (less the extra quid), whereas buying two different tickets gives you two chances to win the Jackpot, so that's a significantly better (while still very small!) expected return.
( flatfrog Staring vacantly into space, Tue 12 May 2009, 13:00, closed)

your missing my point
if there are three winning tickets and you have two the other poor sod is gonna be well pissed off with you
( spimf ™ is whoever you want him to be, Tue 12 May 2009, 13:14, closed)