FACTBOX - Longest-serving prime ministers

(Reuters) - Tony Blair chalked up a decade in office on Tuesday. He ranks ninth on the list of longest serving prime ministers and is only the second person in the last 100 years to have held the job for 10 years.

Here are some facts about prime ministers:

-- Only Margaret Thatcher has outlasted Blair as prime minister in the past century, occupying the head of government's Downing Street residence for 11-1/2 years from 1979 to 1990.

-- Both fall well short of several previous occupants of the post. Sir Robert Walpole, generally regarded as the first prime minister, served nearly 21 years from 1721-42.

-- Blair is the longest-serving Labour Party prime minister and the first to win three elections in a row.

-- One woman and 51 men have passed through the doors of Number 10 Downing Street as prime minister since the address was first associated with leaders in 1730.

-- George Canning holds the record for the shortest term as prime minister, serving just 119 days in 1827.

-- Here's a list of the longest serving prime ministers:

- Robert Walpole: (1721-42) 20 years 314 days.