Orange UK stopped its pay-as-you-go customers from accessing the website of a French civil society organisation which fights against censorship, from their mobile phones.

Jérémie Zimmerman, co-founder of the organisation told civilsociety.co.uk that the most likely reason was that there had been a “simple mistake”, but added that this was exactly the sort of “online censorship” that la Quadrature du Net campaigns against, so he could not discount the possibility that it was “someone trying to harm us” possibly through a user reporting the site as inappropriate.

He added: “In the past we have sometimes taken positions against Orange UK as well as other internet providers.”

La Quadrature du Net campaigns against internet censorship, and at the moment is particularly vocal about the Anti-Counterfeiting Trade Agreement (Acta) which has been negotiated by 39 countries including all of the European Union and the US. This agreement will impose new criminal sanctions forcing internet companies to monitor and censor online communications.

Zimmerman is confident that the organisation will be removed from the blacklist but added that the real issue was that other organisations may not even be aware that they had ended up on such a list.

Orange UK later confirmed that the site had been blocked by mistake by its mobile filtering system but that it had now removed la Quadrature du Net from its blocked list.

A spokeswoman said that the company "was sorry for any inconvenience" but that the "mobile safeguarding filter was there to protect customers who were under 18 from viewing inappropriate content".

The only way to find out if a website has been blocked is to try and access it.