WiFi isn't a guaranteed speed and we're missing out some key details such as distance from hub, devices connected at current, have you tried disconnecting every device from WiFi then restarting your Hub and trying again? Is the 3Mb consistent across all devices including any hardwired devices? Have you checked for any faults in your area?(https://my.virginmedia.com/faults/service-status)
** I work for VirginMedia but all opinions posted here are my own.
