If you consider that an extraordinary meeting can be called by two councillors (where they would publish/produce the agenda), you wouldn't be summonsed to that meeting; the councillors do no have the power to do so. They still require the same notice period to have received the agenda though. The purpose is to give the councillors time to consider what's on the agenda, look into the items, maybe even get some public feedback on any motions... so I would suggest that there isn't an issue on whether the summonsing was done correctly, but I think you'll find that the meeting hasn't been "published" correctly if the agenda and any agenda pack weren't published in the legally mandated time-frame.
Of course, it then becomes a case of what to do about it - if enough of the councillors object and fail to show up, the meeting can't take place. The only other thing you can do is challenge it after the event. If you're in a minority of councillors where a majority are trying to push something contentious through, I would first propose a motion to try to defer the matter until members had time to look at the items in more detail. If that fails, I would ask for the votes of each members to be recorded for those items and then abstain on the grounds that you haven't had time to read/consider the motion. You would then have done everything possible to stop the council taking a vote. Immediately after the meeting, notify the external auditor as to what has gone on. They can intervene if the situation is particularly "dodgy". Failing that, and if you really do believe the motions passed have not been considered properly, you can request a judicial review yourself - but it's a time sensitive and costly process.
