I've been doing the stretches as prescribed by Phil the Phizz and although they made the knee hurt initially, it seems to have settled down again now mostly.
Encouraged by this I went for my long walk/run yesterday morning. I kept to under 5 miles for the running part again, having plenty of long walking breaks of 10 minutes at a time.
It was a very blustery day, but not the gale force winds that stopped me going out yesterday and I enjoyed my time out on my own.
Pretty uneventful, thankfully.
Stretched afterwards in all the right places and the knees felt ok for the rest of the day.

10 miles - 4.5 running and 5.5 walking
Average HR 128
Peak HR 165 (naughty - this is supposed to be base training)
approx 2.hours 20 minutes (forgot to stop watch at the end)