Steve Shaw wrote: But if we leave the EU without a decent trade deal, we are well and truly stuffed.

It's an 'IF' article of course, and if I've got the right one it's nearly five months old. The opinions it expressed don't seem to be part of the current concensus but, as you say, they come up with the cost being £4.5 billion a year.

I did a bit of a search to try and find our current contribution and the best I could come up with was that in 2015 our net contribution was (would be?) over £8.5 billion. I imagine the figure for 2019 would be larger. Let's say that in 2020 it would have been £9 billion. Then a £4.5 billion cost of not paying £9 billion is a saving. Incidentally I also came across an article from 2014 talking about how our contribution was going up by £2.7 billion a year. I can't remember if that actually happened or not but once we leave it won't happen again.