Very wet on the way in this morning, but no problems as virtually no traffic at 6am around here and a good drying unit to get everything (including shoes) dry for home time.
However I went to get the bike out of the lock-up to go home and found a flat rear tyre. Whipped the wheel off and back into the locker room where I keep a pump, patches and tyre levers, out with the tube and ... nothing. no leak found at all. put the tube back in, pumped it up to around 80 psi, still nothing, disconnected the pump and instant deflation! Tube back out and it turned out that the valve stem had detached itself from the tube and was made worse when I pulled the pump head off the valve, so it was back out to the bike and retrieved the spare tube from the saddle pack. All fitted and ready for home about 15 minutes later than expected.