Why does Norway send the UK a Christmas tree every year?

London's Trafalgar Square Christmas tree has been put up, after travelling from Norway to the UK.

The famous tree is a gift from the city of Oslo, Norway's capital city, and forms part of a longstanding tradition between the two cities going back more than 70 years.

The spruce arrived in central London ahead of an official lights switch-on ceremony later this week.

But why does Norway send the UK a Christmas tree every year? Keep reading to find out.

How does the Norway Christmas tree get to the UK?

Lord Mayor of Westminster Robert Rigby (on the left) and Mayor of Oslo Anne Lindboe help cut down the spruce

This year's tree is approximately 60 years old, stands at 20 metres tall and weighs about 1200 kilograms.

It came from a forest in Grefsenkleiva, in the north of Oslo.

It was cut down at the end of November in an official public ceremony hosted by the Mayor of Oslo, Anne Lindboe, and was also attended by local primary school children, as well as experts involved in the conservation of the forest.

The Trafalgar Square Christmas tree is usually a mature Norwegian spruce and between around 50 to 60 years old, due to the size needed.

The tree is selected from the forests surrounding Oslo with great care several months or even years in advance.

The tree then begins a long and complicated annual journey to the UK.

First of all, it is driven more than 60 miles south of Oslo to the port of Brevik.

There it is carefully loaded onto a ship (avoiding any contact with salt water, which could damage it) and sets sail to the UK.

The tree arrives in London a few days before the light switch on so the branches have time to settle

When it arrives in the UK, it is checked by customs officers before being loaded onto another lorry for its ride to central London.

When it reaches Trafalgar Square, a specialist rigging team carefully puts the tree up using a hydraulic crane.

The tree will be decorated in traditional Norwegian style, with vertical strings of energy-efficient lights, Westminster Council said ahead of the official switch-on ceremony on Thursday 5 December.

Why does Norway send the UK a Christmas tree every year?

This year marks the 77th anniversary since Norway sent the first spruce to London

The tradition started in 1947 and is a gift from Norway for Britain's support during World War II.

When Norway was invaded in 1940 the King of Norway at the time, Haakon VII, sought refuge in Britain and the Norwegian government moved to London.

After the war, Norway began sending a Christmas tree to London every year as a way of saying 'thank you'.

The tree symbolises the close friendship between the people of Norway and Britain.