With thousands rushing to buy lottery tickets on Tuesday in the hope of winning Wednesday's £50.4m rollover jackpot, a probability expert has explained why such a huge sum is up for grabs in the first place: the chances of winning have gone from “dreadful” to even more dreadful.

Dr John Haigh, Emeritus Reader in mathematics at Sussex University, said that by increasing the number of balls in the draw from 49 to 59 in October, the National Lottery organisers had reduced the odds on anyone’s six numbers coming up from about 1 in 14 million to 1 in 45 million.

This threefold reduction in the chance of winning the jackpot, he said, helped explain why no-one had won it since 14 November.

As a result, there have now been 13 consecutive rollovers, pushing the prize total up to a record-breaking £50.4m.

There is, however, some good news for punters: if no-one wins the jackpot in Wedneday's draw, Camelot, the National Lottery operator, will for the first time enact new regulations stipulating that the jackpot must be won by somebody.

So if no one’s six numbers then came up on Saturday, the jackpot would go to anyone with five numbers and the bonus ball. If that produced no winners, the money would go to those with five main numbers, then anyone who had four main numbers, and so on until the jackpot was at last claimed.

Feeling lucky? Global lottery odds Mega Millions (America) Chance of winning jackpot: 1 in 258,890,850.

Chance of winning some sort of prize: 1 in 14.7 Euromillions Chance of winning jackpot: 1 in 116,531,800

Chance of winning some sort of prize: 1 in 13 Powerball (America) Chance of winning jackpot: 1 in 292,201,338

Chance of winning some sort of prize: 1 in 25 Oz Lotto (Australia) Chance of winning jackpot: 1 in 45,379,620

Chance of winning some sort of prize: 1 in 55

A £50.4m prize would dwarf the current biggest individual Lotto win of £20.1m, and a Camelot spokeswoman said the repeated rollovers and mounting jackpot total had “generated great excitement in terms of sales”.

Dr Haigh, however, cautioned against getting too excited.

Analysing the odds of winning the lottery after the October rule change, he said: “They were dreadful before, they are more dreadful now.”

He said that adding 10 extra balls to the draw had reduced the chance of a jackpot win from 1 in 13,983,816 to 1 in 45,057,474.

Given that the lottoland website once calculated that your chances of being canonised are very roughly 1 in 20 million, Dr Haigh’s figures would suggest you are now more than twice as likely to become a saint as you are to win the Lotto jackpot with a single ticket.

This perhaps explains why, when the rule change was introduced in October, it was met with opposition by regular players: “‘Extra numbers to choose from.’ That’s a lovely way of saying, ‘Less chance of winning’,” said one.

Camelot, however, insisted that other changes introduced in October had in fact increased players’ chances of winning prizes.

Buying a ticket now gives you a place in the “Millionaire Raffle”, which offers one guaranteed £1m prize. Also, two matched Lotto numbers now wins you a Lucky Dip ticket for a future draw. Camelot said there would be an extra 1.8 million winners a week as a result of the changes, increasing the chance of winning any prize from one in 54 to one in 9.3.

Dr Haigh, however, said: “It’s true the chance of winning something is 1 in 9.3, but the something you win is far more likely to be a ticket for the next draw.

“The chance of winning a cash prize has gone down. For example, the chances of matching three numbers and winning the lowest cash prize of £25 has gone from about 1 in 57 to about 1 in 96.”

If the jackpot is rolled over to Saturday, he said, the chance of winning it by getting six numbers or five and the bonus ball would be about 1 in 6.5 million.