All draw game sales and prize claims will be paused in shops across the UK from 11pm on Saturday after the Lotto and Thunderball draws until “late Monday morning”, operator Allwyn said.
The National Lottery website and app will also be down over the same period.
Allwyn said the “short-term disruption for players and retailers” would allow for the biggest technology upgrade in the game’s 31-year history.
In a message on the National Lottery website, players are being told the upgrade is “about improving your experience over the coming months and years”.
Players are being advised to buy draw tickets, check results and claim prizes before 11pm on Saturday.
They will not be able to log into their online accounts, buy draw tickets or claim prizes – in shops or online – until Monday.
Players will still be able to buy Scratchcards from stores and view the latest draws and results on the National Lottery’s YouTube channel.
Allwyn said the lottery’s gaming and retail systems will move to new platforms – but warned a “small proportion” of store terminals could experience delays coming back up if certain upgrade processes are interrupted.
The Czech-based Allwyn group took over the 10-year licence to run the lottery from Camelot in February last year.
The upgrade will pave the way for “new, exciting games”, an improved player experience and enable weekly returns to good causes to be doubled to £60m by the end of its licence, Allwyn added.
It said the systems and store terminals powering the lottery dated back to 2009, “before iPads, Uber and Instagram” and needed to be modernised to allow for “ambitious” plans.
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Allwyn chief executive Andria Vidler said: “This is a once-in-a-generation opportunity to deliver the National Lottery that the UK deserves.
“We’re making unprecedented and much-needed changes, which will move us closer to achieving our vision for the National Lottery, restoring its magic and significantly increasing its positive impact on lives across the UK.”
