Are There Any Arguments That Hesse Was Not Expected?

If the British were expecting Hesse, they would have assigned a fighter escort to protect him on his way over. The absence of an escort and the attempt to shoot the plane down are strong factors indicating that Hesse was not expected. I can't rule it out that somebody in Britain had advanced knowledge of Hesse's visit, but if so, this person or persons was so marginalized that it didn't affect the situation, and they tried to shoot down the plane anyway.