The stat emblem of great britain

St Patrick's saltire
The reason that the UK flag is not symmetrical is because of the relative positions of the saltires of St Patrick and St Andrew. The red saltire of St Patrick is offset such that it does not relegate the white saltire of St Andrew to a mere border. St Andrew's saltire has the higher position at the hoist side with St Patrick's saltire in the higher position on the opposite side.
Half-mast
The Union Flag is flown from Government buildings at half-mast in the following situations:

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  from the announcement of the death of the Sovereign (an exception is made for Proclamation Day – the day the new Sovereign is proclaimed, when the Flag is flown at full mast from 11 am to sunset)
  
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  the day of the funeral of a member of the British Royal Family
  
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  the funeral of a foreign Head of State
  
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  the funeral of a former British Prime Minister
  

The Sovereign sometimes declares other days when the Union Flag is to fly at half-mast. Half-mast means the flag is flown two-thirds of the way up the flagpole with at least the height of the flag between the top of the flag and the top of the flagpole.
Flying from public buildings
Until July 2007, the Union Flag was only flown on Government buildings on a limited number of special days each year. The choice of days was managed by the Department for Culture, Media and Sport (DCMS). Government buildings are those used by civil servants, the Crown, or the armed forces. They were not applicable to private citizens, corporations, or local authorities.
On 3 July 2007, the Justice Secretary Jack Straw laid a green paper before Parliament entitled The Governance of Britain. Alongside a range of proposed changes to the constitutional arrangements of the UK was a specific announcement that there would be consultation on whether the rules on flag-flying on Government buildings should be relaxed.
Two days later, Prime Minister Gordon Brown announced that with immediate effect the Union Flag would fly from the flag pole above the front entrance of 10 Downing Street on every day of the year. The intention was to increase feelings of British national identity. Other Government departments were asked to follow this lead, and all Government buildings in Whitehall did so.
James Purnell, Culture Secretary from June 2007 to January 2008 in Brown's administration, subsequently concurred with the abolition of the restrictions – pending consultation on longer term arrangements.