These documents are called convention travel documents because they are provided in a way that is set out in part of the 1951 United Nations Convention Relating to the Status of Refugees.  

 

If we have given you humanitarian protection in the United Kingdom you can apply for travel documents if you are unable to obtain a national passport or other identity documents from another country to enable you to travel. You will not be allowed to travel to the country you came from.

 

If you have been granted discretionary leave to stay in the United Kingdom you are expected to keep your own national passport valid. This is because UKBA usually have given you that leave for reasons other than protection.  However you can apply tfor a certificate of travel. You will normally have to prove that you have been formally and unreasonably refused a passport by the country you came from unless you can show us that you have a well-founded fear of the authorities in that country.