The message
from T i m contains these words:

Without Ultraseal your tyre rapidly deflates and if you feel it before
it's too late and can get to safety before you get
chucked_down_the_road you are indeed a lucky man

A puncture big enough to deflate so rapidly that you can't get to the
hard shoulder is in my experience too large for tyre sealants to deal
with.

--
Skipweasel
Pay no attention to that man behind the curtain.