The claim: "We are giving £20bn a year or £350m a week to Brussels."
Reality Check verdict: We are not giving £20bn a year or £350m a week to Brussels - Britain pays £276m a week to the EU budget because of the rebate.
He has gone with that figure despite a letter from the head of the UK statistics watchdog Sir Andrew Dilnot on Thursday, which described it as "potentially misleading".
The figure used is roughly the UK's gross contribution to the EU - the amount that would be contributed to the EU Budget were it not for the rebate.
We say "roughly the UK's gross contribution" because the annual figure that Boris Johnson used was £20bn, somewhat higher than the £18.8bn figure for 2014 - the most recent figure available - while the £350m a week figure is a bit below the actual figure of £361m.
The important point is that it's not the sum we send to Brussels because the rebate is deducted before any money is paid. In 2014, the UK's contribution to the EU budget - the amount we paid to Brussels - was actually £276m a week.
If Britain were to give up the rebate, then the UK would have to pay the gross contribution, and it should be noted that the rebate is not a permanent feature of Britain's membership of the EU.
But we do not pay the gross contribution at the moment, the rebate is safe until 2020, and Britain has a veto over the process that would remove or reduce it.
Sir Andrew Dilnot is particularly concerned about suggestions from Vote Leave that a sum of money equivalent to the gross contribution could be spent on other priorities such as the NHS, when some of it is not spent at all (the rebate) and some of it is currently used to support UK farmers, for example.
READ MORE: The facts behind claims in the EU debate

The incident happened at about 15:30 BST on Friday on the Albertbridge Road.
The man who died was Patrick McDermott from east Belfast.
Police have appealed for information in relation to the incident.

Initial attempts to free the animal by slathering him in olive oil failed, with his huge behind preventing him from squeezing his way out.
He was finally freed after animal rescue services lifted off the cover and eased his head through the hole.
Locals have nicknamed the squirrel "Olivio" after his oily encounter.
After the ordeal on Friday, an exhausted Olivio was wrapped in a warm towel and fed glucose, local media report.
Man rescued from inside public toilet
Squirrel causes major power cut
Staff at a local animal shelter say Olivio is recovering well and has now moved on to a diet of Christmas nuts.
"He was almost dead," Sabine Gallenberger from the Squirrel Protection Association told German media.
"Now he is eating a lot and sleeps all the time."
The BBC was unable to verify the size of Olivio's behind.

It follows recent controversy over MLAs' expenses.
The Assembly Commission has asked IPSA, the Independent Parliamentary Standards Authority, to update a report on the Stormont system it compiled last year.
The commission held a meeting on Wednesday to discuss the matters raised over the last few days.
There was a public row between the Independent Financial Review Panel, which sets MLAs' allowances, and the Assembly Commission, which administers the expenses system.
The IPSA report of September 2015, which was leaked to BBC Radio Ulster's Nolan Show, called for changes in the way the assembly reviewed expenses claims which had initially been refused.
But the Assembly Commission, which is made up of the Speaker and MLAs from the five biggest parties, has made the point that the report, in its own words, "did not identify any major issues of concern".
The recommendation about the assembly's review procedure is one of a "small number" of recommendations which the assembly authorities say they are acting on.
The changes recommended in the IPSA report are to be added into the MLAs' handbook.
IPSA will examine the new handbook to "quality assure" it before it is approved by the assembly.
In Wednesday's meeting, the commission also confirmed its intention to develop plans for legislation to "strengthen the effectiveness" of the Independent Financial Review Panel.
Mayor of London Boris Johnson used the figure in The Sun this morning that the UK gives £350m a week to Brussels.
[NEXT_CONCEPT]
A 79-year-old man has died after being struck by a lorry in east Belfast.
[NEXT_CONCEPT]
A red squirrel who got stuck halfway through a manhole cover thanks to his curvy hips is recovering after a lengthy rescue operation in Munich.
[NEXT_CONCEPT]
The cross-party body which runs the assembly has asked the Westminster expenses regulator to do some more work reviewing the Stormont expenses system.