//All EU members need to approve an extension and the question being asked is whether the UK could veto it and thus leave on 31.10.19 as planned.//
//Better legal minds than mine can spend their time arguing the point, but for my part, once the UK has made a request for a given date then it must surely stand to reason that it has agreed to that date.//
Please see my answer at 20:14 yesterday (seems a lifetime ago).
//….and lose our veto//
Wasn’t going to go over old ground, Jim, but you continually mention “our veto”.
Individual EU member nations, when voting in the EU Council, no longer have any effective power of veto in all but less than a dozen policy areas. The Treaty of Lisbon abolished the requirement for unanimity in no less than 45 policy areas. These include asylum, immigration, border controls, criminal law, the ECJ and social security. Among the few still requiring unanimity are the admission of new members, taxation and citizenship. However, the European Commission has its sights set on abolishing as many of those as it can (plenty of info available online. I can’t be bothered to look).
These vetoes are available to all member nations. I don’t know of any that are specific to the UK which have been retained as “grandfather rights”.