Selfridges says it is "very disappointed" at the actions of a member of staff who allegedly refused to serve EDL leader Tommy Robinson and a friend.
The flagship department store said Robinson should have been made to feel welcome when his friend tried to purchase designer clothing.
A shop assistant has been suspended after the far-right activist claimed his companion was told to "fuck off".
The EDL chief, real name Stephen Yaxley Lennon, videoed the encounter and posted it on Youtube.
In a statement, Selfridges told HuffPost UK: "We pride ourselves on making everyone welcome and endeavour to provide world-class customer service at all times.
"We are therefore very disappointed at the incident which occurred this morning.
"We are taking the matter very seriously and are currently investigating it."
After hearing of the incident many people took to Twitter urging people to email Selfridges and congratulate the man for refusing service.
But the store confirmed to the Huffington Post UK that its disappointment was aimed at the shop assistant, who is still suspended as an investigation takes place, because all customers should be made welcome in its stores.