Chaotic scenes unfolded as police deployed dozens of officers to contain potential trouble when ex-EDL leader Tommy Robinson made an appearance.
Mr Robinson was confronted by people who held opposing views and officers escorted him away as he told people they "hate free speech".
UAF protesters chanted "EDL go to hell" as protesters spilled on to the road.
Scotland Yard said 14 people had been arrested for "various offences" by the time the protest tailed-off at 4pm.
Crowds had gathered in Trafalgar Square from around midday to follow a route set out by the Metropolitan Police.
As the march made its way down Whitehall, police lined the route and as a scuffle broke out a medic could be seen dealing with someone on the ground.
Officers manning safety barriers battled to keep opposing sides 100m apart.
Britain First supporters listened to a speech - apparently protected by their own security guards - before marching through the roads shouting "terrorist scum off our streets".
On a Facebook event page, Britain First said "all patriots welcome to attend", while the EDL said on an event page: "After the vile terrorist attack on parliment we will stand together and show we will not now, not ever bow down and fear terrorists and terrorism. Join us to show our strength."
The event took place just over a week after Westminster terrorist Khalid Masood's murderous rampage left four people dead.
Many people took to social media to mock the poor turn-out for the far-right march with some commenting that there had been more police officers than supporters.
Others noted the fact the rally took place on April Fool’s Day.
So the EDL and Britain First come out for a march on April Fools day. Appropriate. 😂— Gerald Mung (@Tigzy_J) April 1, 2017
One user wrote: “Just seen on Channel 4 news about the EDL/Britain first March in London.
“Pathetic numbers on Westminster Bridge, more police protecting them.”
Britain First are protesting on April Fools Day. Glad to see Britain's sense of humour is still going strong— François Budapest (@FeewoodMac) March 25, 2017
Comedian David Badiel added: "EDL march means police blockade outside. Over soon but I'll do show on @ThePlayhouseLDN roof if necessary."
Jamie Roberts added: “Embarrassing "March" by #EDL I've had more people in my living room at one time.”
Dan Green said: “Shoutout to Britain First and the EDL for having a march on April Fool’s Day. Showing what a joke they really are.”