Deadline for accepting offers

When do we have to respond to our UCAS offers by?

And in UCAS, am i right to say that we just need to indicate which is our firm and insurance choice?

June 7th. See here.

Yes, though having an insurance choice isn't compulsory, or you could decline all your offers if you wish.

When do we have to respond to our UCAS offers by?

And in UCAS, am i right to say that we just need to indicate which is our firm and insurance choice?

Isn't it May 9th if all offers have been received by March 31st? Apart from internationals and Extra applicants?

Edit: Sorry, just spotted Singapore, so it is an international as you so rightly saw. However, I'll leave this here in case any non-internationals see June 7th and think that applies to them.

Edited my post to clarify it