Confidence: I'm as sure as I can be.
Notes: a female, from the ovipositor. Definitely not Pimpla rufipes (formerly called Pimpla instigator) which has a much shorter ovipositor. Could be a number of species belonging to the subfamilies Rhyssinae (e.g. Rhyssa) or Pimplinae (e.g. Dolichomitis) etc. etc. It's a pity that the specimen appears to be backlit, so there is little detail.