As you can see from the scale on the base of the bug box (left) she is about 1cm long with an ovipositor that’s as long again.
She seemed to be a wasp with a mission, busily pacing up the window, pausing only to bend the long ovipositor over for cleaning. I can’t remember now if she held it bent beneath her or over her back. I think the latter.
Just in case there’s anyone out there who can identify the species for me, I’ve included this close up of the wing, as I understand the wing venation is one of the keys to identity. I wasn’t able to take a decent side view.
The nearest I can see in the book is the Large Ichneumon Lampronata setosas but that is getting on for twice the size. This looks like a close relative. The Large Ichneumon uses its long ovipositor to drill into wood to lay its eggs on the larvae of the Goat Moth.
Update; Thank you to Graham for suggesting Rhyssa persuasoria as the species. This is sometimes known as the Giant Ichneumon but a female would normally be two to four times as long as the specimen I drew.