Great reviews of Jethro Tull and Fairport Convention,
Morthoron. Both very fitting, I'd say.
Nightwish covered a song by Gary Moore that is steeped in British military tradition, with versions going back over several centuries. Moore's and Nightwish's lyrics aren't exactly Tolkienish, based as they are on adultery and deceit (a sort of British 'Long Black Veil', without the capital punishment), but the haunting melody and drums evoke for me a sense of Middle-earth. Nightwish brings in Viking elements while Moore brings in Celtic.
Here's some YouTube versions and then a link to the traditional versions of the song.
Gary Moore's Over the hills and far away
Nightwish's Over the hills and far away
Over the hills and far away--traditional versions