A socialist bookshop says “fascists” wearing masks threw books around and attempted to “intimidate staff and customers”.
Bookmarks, in London’s Bloomsbury, claimed about a dozen far-right protesters arrived just before it closed on Saturday.
Staff were called “traitors” and books “ridiculed and thrown around”.
Police were called but no arrests were made.
The shop said on Facebook: “On Saturday evening around 6:45 just as we were closing, Bookmarks was attacked by around a dozen mask wearing fascists.
“They attempted to intimidate staff and customers and to destroy books and materials. Fortunately no one was hurt.
“We will not let this happen! Never Again!”
The shop added on Twitter: “This is the true face of fascism. No Pasaran! (They shall not pass)”.
Hundreds of people wrote messages of support after the bookshop urged its followers to “send solidarity”.
According to anti-racism group Stand Up To Racism (SUTR), some of the protesters held placards which read “British Bolshevik Cult”, while one wore a Donald Trump mask.
Books on Islamophobia were “ridiculed and thrown around”, a member of staff told SUTR.
“They chanted about Muslims and paedophilia, and called us traitors,” the worker added.
The protesters also shouted about Jeremy Corbyn and anti-Semitism, SUTR said, while threatening to return and “show what they can do”.
In addition, they allegedly picked up a book called The Jewish Question by Abraham Leon, “holding it aloft as proof of the anti-Semitism of the left”.
“Luckily no one was hurt this time, but this is a sinister development that indicates the growing confidence of the far-right who feel they can attack a bookshop in central London in broad daylight,” said Michael Bradley from SUTR.
“Attacking a bookshop also exposes their claims to be defenders of free speech as hollow.”
Ealing Central and Acton MP Rupa Huq described the incident as “utterly despicable”.