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That looks like a solitary wasp, and an ichneumonid, but I can't work out which one. None of these quite seem to fit, perhaps the closest is amblyteles armatorius (but as the guide isn't complete, it may not be in there):
https://www.naturespot.org.uk/sites/default/files/downloads/british-ichneumonid-wasps-id-guide.pdf
Shame you didn't get a picture of the hornet. Hornets and wasps are much less aggressive close to their nests than honeybees, by the way.
Oliver Schick-
Maybe a giant wood wasp? Would make sense of the abdomen rubbing against the bark:
The giant horntail is a massive sawfly that is also known as the 'giant woodwasp' or 'greater horntail wasp'. A relative of the wasps, the female is black and yellow and has a long, stinger-like tail that is actually her ovipositor, which she uses to lay her eggs into wood, particularly pine. The larvae live in the wood of pine trees, where they spend up to five years developing. Found near pine woods, or places where pine timbers are used.
How to identify
The giant horntail is a black-and-yellow-banded insect that looks like a large wasp, so may be confused with the hornet or hornet robberfly. The female has a long ovipositor at the end of her body, which looks like a stinger.Taken from: https://www.wildlifetrusts.org/wildlife-explorer/invertebrates/bees-and-wasps/giant-horntail
eskay
Stopped while out riding at the weekend and leant my bike against a log pile. The biggest hornet I have ever seen buzzed out and landed on my tire. I couldn't get a pic quick enough before it buzzed back into the pile. There was also this one that was frantically rubbing its abdomen against a log for some reason.
Very wary of being that close to a potential hornet nest so made a quick exit.