Shops were attacked, passers-by threatened and car windows smashed during a demonstration in central London against the election result in the Democratic Republic of Congo.

The carol concert was raising money for MacMillan Cancer Support. It was organised by a group of friends whose loved ones had been treated for cancer.

Masked teenage boys ‘stormed’ the singers, throwing bottles of water and hot drinks into the crowd. A woman in her 40s, said to be undergoing treatment for breast cancer, was pulled to the ground. A youth attempted to set light to the Christmas tree, an annual gift from the city of Oslo since 1947, one witness said.

“They were determined not to let us sing and have fun and utterly ruined the atmosphere. Have your protest and make your point, but why did you have to ruin a lovely occasion with your scuminess,” Mark Horton, a conductor of the choir, wrote in a message online. The concert was cut short amid safety concerns.

The attack was ‘egged on’ by teenage girls who screamed and shouted “like the possessed”, another witness said.

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Police made 110 arrests for affray as fights broke out between demonstrators.

Other arrests were made for assaulting police officers, obstructing police and blocking a public highway. Police held demonstrators inside double decker busses before ferrying them to custody.

The demonstration began as an agreed ‘static’ protest in Whitehall on Saturday evening against the re-election of President Joseph Kabila, which international observers say “lacks credibility”.

The vast central African country has immense mineral wealth but has been ravaged by civil war, corruption and economic mismanagement. Protestors accuse Western governments of propping up the regime.

On Thursday a group of 200 Congo demonstrators forced the evacuation of Oxford Circus tube station, central London, after they set off a passenger alarm on an underground train.