With Virgin I’d recommend turning off the WebSafe filters.

• log-in to My Virgin Media – http://my.virginmedia.com – as the primary account holder.
• Go to the My Apps section, and select Parental Controls with Virgin Media Web Safe.
• Click on the Manage Web Safe button.

First turn off the Child Safe filter. If that doesn’t help, you’ll need to try turning off Virus-safe. Please note that doing so will reduce your online protection, but as Virgin has included some sites in their blacklist that aren’t dangerous, this is the only simple approach.