Lotto ticketholders with five numbers in Wednesday's draw were left frustrated after they won less money than those who matched only three.
Camelot said more than 4,000 players matched five of the six balls to win £15 each.
This was compared to the 7,879 ticketholders with four numbers who won £51, while the 114,232 people who matched just three balls won £25.
No one scooped Wednesday's Lotto jackpot, sending Saturday's prize to an estimated £28.2 million.
Some Lotto players vented their frustration on Twitter about the unusual situation, which can arise when there are a large number of lower prize winners because the minimum win is set at £25.
Leon Howell ?tweeted: "So getting 5 numbers in the national lottery tonight bagged you £15 but 3 numbers got you £25......thenationallotteryrobbery."
Matt Needham wrote: "3 numbers tonight = £25. 5 numbers tonight = £15. The national lottery is an actual joke!!!!"
Conor King added: "Match 5 numbers with odds of over 1 in 144,000... Win £15. The UK lottery is officially a joke."
The winning Lotto numbers were 14, 21, 42, 35, 07, 41 and the bonus number was 43.
Six ticketholders matched five of six balls and the bonus ball to scoop £10,016, while 4,082 players matched five of the six balls to win £15 each.
There were no jackpot winners in the Thunderball. The numbers were 33, 26, 27, 38, 23 and the Thunderball number was 13.
There were two jackpot winners in the Lotto HotPicks draw, each scooping £350,000.