Any far and open-minded scientist would agree that UFOs should be studied. We do not know everything about our planet's atmosphere and there must be rare phenomena yet to be discovered.

But the thing that has frightened many scientists away from such a sensible attitude towards UFOs is that most people think that a UFO is the same thing as a flying saucer.

I would like to believe that our planet is being visited by aliens but I cannot.

Why is it that all of the thousands of photographs and videos purporting to be of 'flying saucers' are out of focus? Surely someone must have taken a close and detailed picture?

Ask an advocate for evidence that aliens have landed and you will get one of two things in reply. You will get stories and you will get excuses.

Some of the stories are interesting. You can talk to people who say they have been for a ride in an alien spaceship, some of them claim to have been molested and experimented on by aliens.

But a story is just a story. I cannot believe them unless there is supporting evidence.

Then there are the excuses. When you ask for proof that our world is being visited by aliens you get all sorts of reasons why such evidence exists but cannot be produced.

It is a cover-up they say. We did have evidence but it was stolen by government agents who are part of a great plot by the authorities to conceal the truth.

We have all heard about the claims that alien bodies are stored in deep-freeze in a secret vault in a United States Air Force base. Supposedly they have been there for 50 years following a flying saucer crash. It has been kept secret ever since.

Well not quite. It is so hush-hush that we all know about it. Questions should obviously be asked about the United States Air Force's ability to keep a secret.

What is lacking is tough-mindedness and an attitude that remarkable claims require remarkable evidence.

I will not believe it unless someone produces an artefact that cannot be man-made; unless someone can pass on information about the universe that we did not know and can be verified.

Or unless they land on the Whitehouse lawn - either the one in the United States, or mine.