It is of course entirely possible that the European Union are genuinely expecting this:

Sir Ivan says the European Commission genuinely expects a figure "of the order of 40-60billion euros" for leaving the EU. 

He says senior figures have said Brexit has "exploded a bomb under the multi-annual financial framework" and left a "big hole" in the EU budget.

The bill would most likely include the UK’s share of outstanding pensions liabilities, loan guarantees and spending on UK-based projects.

And they should of course, as we've mentioned before, be met with a certain amount of pushback. For example, loan guarantees are not things which are payable until the loans sour. So they can be left off said table at present. Similarly, future EU spending on UK based projects is not going to happen thus there is no need for us to pay them for that.

However, the large point here is that the EU itself has some capital value. There are parliament buildings (too many of course but still) embassies, office blocks and so on all of which belong to the institution itself. Which we have helped pay for. In fact, as nearly the only country to have consistently been a net contributor to the overall budget we've paid for most of those things.

And as we're cashing out then we'll have that capital value back, thank you very much. Shouldn't lead to the EU having to pay us too much for leaving but it really is most unlikely that the capital value is less than those accruals, isn't it?