The Strangerers (TV series)

Aliens in human form land on Earth to carry out a secret mission, and when the Supervisor is decapitated, the two bumbling Cadets have no idea what the mission entails. With a mixture of their of own language, and mannerisms taken from old 50s movies, they try and get through the crazy world we live in, without trying to get caught by the various shady organisations after them. - IMDb