The Sovereign Military Order of Malta: Is this the world's most exclusive passport?

The Sovereign Military Order of Malta is one of the world's rarest passports.

Although the group is made up of more than 90,000 people, only one permanent ordinary passport is issued at any time - making it the world's most obscure travel document.

Twelve other people hold a temporary version for their five-year term. The Order also issues diplomatic passports for official business - about 500 of these are currently in circulation.

So, who are the mysterious Sovereign Military Order of Malta?

For a start, they are based in Rome, not Malta, and are an apolitical religious order of the Catholic Church made up of more than 13,500 knights, dames and chaplains. It also includes 80,000 volunteers who carry out charitable work around the world, plus 25,000 employees, mostly in the medical profession.

The Order of Malta is self-described as "faithful to its centuries old mission of service to the vulnerable and the sick," running medical, social and humanitarian projects in 120 countries.

In 1113 it received formal acknowledgement as a religious order, making it one of the oldest institutions in Christian civilisation.

Although the passport is unique, it is not accepted in some countries including the US and the UK. According to the Order, the diplomatic passport though it is recognised by 106 countries including large European countries such as Germany, Spain, Italy and Poland.

Germany still holds the world's most powerful passport, in an annual ranking carried out by Henley & Partners, a citizenship and planning firm, which takes into account how many countries can be visited without needing a visa.