The Brexiteers are getting increasingly vocal in their demands that the UK should be preparing to walk away from the EU talks with no deal, keeping the Â£39 billion (or whatever the final figure is) that the UK has already agreed to pay in settlement of existing contractual commitments. They are seriously arguing that the UKâ€™s hand in negotiations will be strengthened if the EU believe that the UK government is really serious about being willing to walk away with nothing at all in March next year.
Itâ€™s an â€˜interestingâ€™ idea (Sir Humphrey would probably call it â€˜braveâ€™) that threatening to renege on commitments already made and to walk away from treaty agreements will make the EU27 more willing to offer a super-duper deal to the UK which surpasses anything offered to any other non-member of the club. Because thatâ€™s what theyâ€™re actually suggesting â€“ under the EU treaties, the UK and the EU are obliged to negotiate terms for withdrawal and settlement of agreed obligations; there is absolutely no requirement for the EU27 to offer any sort of trade deal in exchange for the UK meeting its existing treaty obligations.
In those circumstances, itâ€™s not at all clear to me that making such a threat will encourage the EU27 to be more flexible in order to secure an agreement â€“ it seems much more likely that it will serve only to convince them that the UKâ€™s word cannot be trusted, and that no promise or agreement is worth the paper on which it is written. To be blunt â€“ who on earth would want to negotiate with someone who sees going back on their word as a legitimate tactic? They could never be certain that any agreement would be honoured.