thanks for taking the time to reply, but it's gatorskins that are currently causing me grief.
Yet another this morning.
Back tyre again.
In the middle of the tread,
nice neat hole through the seam of the tube.
I am becoming a fully paid up member of the "two spare tubes and repair outfit" brigade. Who knows in a few years I might end up like some people I know with a whole workshop in a roll on the back next to the bivvi and flea bags!