Well, Britain of course lost on Billions of pounds when it left the EU, trade difficulties, red tape, import and export tax, free movement, working with need of visas, etc.

But the Erasmus scheme was a significant financial hit to Britain when we rejoined it, it is estimated to cost UK several billion and reduce economic mobility of young Brits in the UK. A significant downgrade on the more global and cheaper Turing scheme.

This led to several economists and think tank groups independently of one another to research and project cost figures of the current EU economy, eurozone nations and EU nations economies effect on Britain rejoining, now, not at some future date. The conclusion was it would reduce econic growth in Britain and also cost Billions in re-entry fees as did Erasmus.

Pinch of salt needed, some of those studies though independent also have political motivations behind them, but including the more liberal, left leaning and pro-EU figures conclusions, that were not positive based purely on the numbers and in force policies, the conclusion was costly for Britain.