The SXSW London festival has been slammed for failing to defend American political commentators Cenk Uygur and Hasan Piker after the British government banned them from entering the country to speak at the event.

Piker called SXSW "actual fucking losers", and some speakers have dropped out in protest over what they say is SXSW's failure to stand up for free speech.

The two were scheduled to speak at the Oxford Union and SXSW London, a major cultural festival.

Prominent British politicians have condemned the ban as an attack on free speech, accusing the government of targeting criticism of Israel.

While the Oxford Union has condemned the government's decision to ban the two speakers and vowed to allow them to speak over a livestream, SXSW's markedly different response has been widely criticised.