Smiths Tax Take Increase Principle

Why does the day on which self employed people in the UK must pay their taxes fall just after Xmas when all their money has been spent and they have spent two week earning nothing?
They must be extremely tempted to say, ‘no taxes to pay this year’, and leave the government short of funds.
Better surely, to have that day in June, before the summer holidays, when they are more likely to have money in the bank. This will mean I think a much bigger tax take for the government at a time when the budget deficit is close to record levels.