Claim: Leaving the EU would make an average holiday for four people to the EU £230 more expensive in two years.
Reality Check verdict: It would be reasonable to expect a weaker pound to make foreign holidays more expensive, but it is hard to predict a precise figure.
Actually, only the starting point of this analysis comes from the Treasury - Monday's document from the Treasury predicted that if we left the EU, the pound would be 12% weaker in two years than it would have been if we had stayed in.
The 12% figure is not excessive compared with other predictions.
Some banks have been forecasting much more severe declines in sterling if the UK leaves the EU.
The next step was to get the Office for National Statistics to work out the average cost of a holiday for four to various destinations, based on the International Passenger Survey.
Then, you work out how much extra that holiday would cost if the pound was worth 12% less.
And the result you get is that the average eight-day stay in the EU for four people (that's any group of four, not necessarily a family) would cost an extra £230 due to currency movements.
In addition to the currency effect, the release from Downing Street also refers to the chances of air fares increasing following a Brexit, which the Reality Check team has considered before.
We concluded that leaving the EU could lead to an increase in fares, but that the impact could be reduced or even avoided depending on what agreements the UK reached with the EU and other countries.
The release also refers to the cost of mobile phone calls if roaming fees are not abolished.
From next year, mobile phone roaming charges will be abolished across the EU, saving UK customers up to 38p per minute on calls.
But if Britain left the EU, it is possible the UK and Brussels could agree a new deal.
Read more: The facts behind claims in the EU debate
Prime Minister David Cameron has warned: "If we were to leave, and the pound were to fall, which is what most people expect and what the Treasury forecast, that would put up the cost of a typical holiday for a family of four to a European destination by £230."