The bigger bottle will contain beer aged for at least six months, while the current 33cl bottle contains a brew aged for three months.
St Stefanus is brewed by the Van Steenberge brewery and the St Stefanus monastery, and was launched in the specialist off-trade and the on-trade in October.
It is a 7% abv unpasteurised high fermentation beer.
Miller Brands trade marketing director Lucy Jordan said: “Craft beers are increasing in popularity – the off-trade specialist beer market is growing at 21.4% according to Nielsen, compared to 3.1% for the total market.
“St Stefanus is aimed at consumers who are passionate about craft beer and will seek out new, artisan products for a different taste experience. Belgian beers are particularly popular and command a 52% price premium over the average bottled lager in the off-trade, according to Nielsen, so there is a real opportunity to profit from consumers trading up.”