According to the latest estimates, there are about 100,000 people in the UK are living with HIV, although experts say a quarter of those who are infected do not know they have it.
In 2011, there were around 6,000 new diagnoses of HIV in the UK.
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Buckingham Palace, London's Tower Bridge, Old Trafford and Big Ben are taking part in the event to raise awareness about climate change.
Widespread frost for most areas as temperatures dip below freezing.
Premier League clubs have agreed to pay all full-time staff the living wageof £9.15 an hour in London or £7.85 an hour outside the capital.