I think this statement belies that, Nigel.

"Two years on from the referendum, we now know that the Brexit vote has seriously damaged the economy,” said CER Deputy Director John Springford, who authored the study. “We know that the government’s Brexit dividend is a myth: the vote is costing the Treasury 440 million pounds a week, far more than the U.K. ever contributed to the EU budget."

The key points here is that it is costing (NB - costing, not will cost) the treasury more than it pays out in EU contributions. No speculation involved.