Were you charged? Or are you assuming you were charged? You
shouldn't have been, unless you went shopping or something while
outside the barriers for more than 30 minutes (I forget just what the
time limit is in these cases, but it's more than adequate).

I passed between barriers in under 90 seconds.
Maybe I wasn't charged twice and I've done my maths wrong but I'm pretty
sure for some odd reason I was.

Why you didn't walk to Warren Street or get on a 'bus is another
question :-)

As I've said, my feet were aching like never before (I've developed a heel
problem in recent weeks) and just wanted to sit down for a couple of minutes
without stopping moving.
Thus, didn't want to dodge traffic crossing Euston Road, stood waiting for
traffic lights or walk the few minutes further to Euston.
In a way, I didn't think it through but I didn't expect to have to explain
myself !!!! ;-D
Thanks for the suggestion anyway. I'll check my usage the next time I
top-up.