The Russians claim an Ukrainian Su-25 was tailing MH17 closely just before MH-17 was shot down, at the 31K foot altitude the Su-25 couldn't sustain very long. Perhaps the UK military was using MH-17 as an unwitting shield of sorts, either to ensure that their Su-25 wouldn't be shot at, OR (worse) to goad the separatists into firing a missile which could be then lured toward MH-17. It would also explain the slight redirection by ATC which Kiev has been apparently unwilling to release.
A thought...