British and Polish cultures seem so different, but there are some celebrations that are related. Ash Wednesday is the first day of Lent in Christianity. Lent is a time of fasting, so we spend the last days of Carnival on feasting.
In Poland we celebrate Tłusty Czwartek ("Fat Thursday") on the last Thursday before Ash Wednesday. Pączki, full-sized doughnuts filled with rose marmalade, are consumed in large quantities. It's believed to be a bad luck if you don't eat a doughnut on Fat Thursday.
In the UK people celebrate Shrove Tuesday (Pancake Day) on the last Tuesday before Ash Wednesday. The name comes from "shrive" which means "confess", as people used to confess their sins before Lent. The other name comes from the tradition of eating pancakes on that day.