This year my yearly leap through burning hoops at the local immigration office, to extend my non-imm O visa (because marriage), falls on 8th June. However I have today got my three-monthly "receipt of notification" slip of paper which lasts until 21st May.

So my question is: if I turn up on 21st May for my next "receipt of notification" and get it stamped for (say) 21st August, will I have to return on the 8th June for the full Stasi-basement grilling session involved in the yearly visa extention process (because marriage), or can I put back the evil day until 21st August (ie the limit of my three-monthly sign-in)?

If there's a simple, definitive answer to this, it may be the first time I've ever seen one on a visa thread!

Thanking you in advance ...

You can apply for extension early, your new extension will start when old one expires.

I do mine 2-3 weeks before every year.

You must do your extension by the 8th of June. The 90 day report does not change that.

You could do your extension and 90 day report on the May 21st to save a trip to immigration.

That answers it nicely! Trebles all round!