Scuffles have broken out in Trafalgar Square on Armistice Day as thousands of football fans descended on the capital ahead of the England v Scotland World Cup qualifier.

Blood pouring from one fan's leg covered a Saltire flag as paramedics attended a concussion, while at least one fan was taken by ambulance from the scene where thousands of Scotland fans had gathered.

Blue flare smoke hung in the air and the sound of breaking glass could be heard, as police pulled away a group of England fans who looked ready to fight with a handful of Scotland supporters.

About 14,000 Tartan Army supporters were expected to flock to London for the sell-out game at the 90,000-capacity Wembley stadium.

Fans in the central London square sang songs and waved flags, with many climbing onto Nelson's Column and chanting.

There had been no arrests as of 4.30pm, the Metropolitan Police said, but there was a considerably increased police presence in the square.

Public toilets had to be closed at 4.30pm due to deliberate damage such as equipment being kicked and tiles being pulled off, police and workers said.

There were two arrests in Trafalgar Square, one on suspicion of common assault and the other on suspicion of being drunk and disorderly, the Metropolitan Police said.

Police urged football fans to respect Armistice Day events ahead of the World Cup qualifier.

A Met Police spokesman said: "We are aware that in the past Scottish supporters have congregated in Trafalgar Square.

"Given the match falls on November 11, we have also been liaising with the Royal British Legion, who will be hosting their 'Silence in the Square' event in Trafalgar Square to mark Armistice Day."

England fans were promised an early look inside the Three Lions dressing room. The official Twitter feed of the #England football teams, @England, revealed a picture of an England shirt hanging on a hook.

Scotland Yard said it would use the football unit Twitter account (@MPSFootballUnit) to liaise with fans through the day.

Superintendent Alex Carson, who is co-ordinating the British Transport Police (BTP) operation, said: "We want fans to enjoy themselves and for everyone to have a safe and peaceful journey, but we will have a highly visible policing presence to ensure any anti-social behaviour or crime is swiftly nipped in the bud."

Crowds in the square, which had been full for most of the afternoon, started to thin at around 5:30pm as hundreds started making their way on to Tube trains bound for Wembley.

Cracked bottle-necks and empty cans crunched underfoot as they left the square.

Scores of people came down from the column, leaving shattered glass, wet cardboard and spilled alcohol on the landmark. One of the lions flanking Nelson's column had a traffic cone placed on its head.

Passer-by Nicoletta Morelli said: "It's not so nice to see London like this. I have not forgotten the hooliganism of British fans in Rome."

Gillian Johnson, a heritage warden with the GLA, said it was "terrible", adding: "It's really not fair, this is supposed to be a public place."

A foreman cleaning the mess said he had come to "expect this level of mess" when football fans are in town.

Men with large brushes swept away the debris as a strong smell of stale alcohol lingered in the air.

Empty bottles lined the pool rims of the two fountains, which had been switched off after they were filled with fairy liquid by Scottish fans three years ago.

Earlier in the day, shortly before the 11am Armistice Day silence, a group of 22 servicemen from all over Scotland congregated at King's Cross.

Kenny Petrie, 45, said: "We travel for games as a group quite often - this year we've been to France, Prague and Malta.

"We've never had any trouble in England, but there is more friction in Europe, like at the Euros.

"England are trying to escape the hooligan stereotype. We just want a peaceful game and a Scottish victory."

Andy Robbins, 48, a football coach, said: "It's a double-edged sword, Remembrance Day. If anything does happen, it'll be tainted by who's to blame.

"With regards to the football, I think England expect too much."