What "legal" conundrum?

"There is no precedent for a net contributor leaving the EU without paying their dues."

The EU Treaty of Lisbon outlines the procedure for member states who wish to exercise their sovereign right to leave the EU. It is described in Article 50 of that treaty - oddly enough Shaw it makes no distinction between net contributor states and non-contributing states. It is against WTO rules for the EU to make that distinction.

"It is by no means settled that we can leave without paying and that'll be that."

Neither the EU or the UK have signed any paper that binds them legally to pay compensation - if there is please refer me to it. Any such payment must be arrived at by mutual agreement - now believe it or not Shaw that involves dialogue - it is NOT simply a case of the EU Commission in the shape of Juncker, or Barnier, plucking a figure out of thin air and demanding that the UK pays that. It is NOT for the Prime Ministers, or Finance Ministers, of the other EU member states to closet themselves in some chamber and decide what the UK must pay then simply demand that sum - It is for whoever is negotiating on behalf of the EU AND THE UK to agree what that figure is - Now then Shaw IF the EU want anything then they had better start listening to what the British negotiators are saying is necessary for starting those negotiations relating to payments. Which I suppose that is why the EU rules require that the whole process cannot be split up and sub-divided as they have done with result that talks and progress seems to have stalled.

It is a process of dialogue, it is NOT for the EU Commission to set preconditions. While they may THINK that they can lord it over the entire process, they had best realise without doubt that in the forthcoming negotiations (If they expect the UK to stump up) then they had best start treating the UK with a bit of respect, refrain from talk of "punishment" (Juncker, I believe), and approach these talks as equals. As it is the EU who expects the UK to pay them they should be aware of the "Golden Rule" - It is the UK's GOLD.