Thanks David and Wurzel - and a happy new year to you both.
Storm Eleanor seems to have caused total havoc in my woods, with trees fallen all over the place and branches scattered everywhere:

(part of our usual daily walk ...)

(a little sallow corner, completely taken out by a fallen tree - I have often found purple emperor eggs and caterpillars here)
As you can see, warm winds (and rain) have melted most of the snow at this altitude.
Passing some wych elm I saw several branches had been broken. I was wearing the wrong clothes to go digging around in the brambles and other undergrowth, but a quick check on a few fallen twigs revealed some white-letter hairstreak eggs:
I took them home to keep in the fridge for now. Advice on how best to proceed to give them (and the others I shall go looking for) a chance of living would be greatly appreciated.
I examined one egg under the microscope at home. It was difficult to take photos (I used my iPhone, straight down the eyepiece...) but I think this egg might not be viable anyway, as it seems to have a tiny hole:
The hole is at about 4.00 o'clock in this image:
It was difficult to get the iPhone to focus on the hole itself, but it did really look like a tiny perforation through the microscope.
Guy