Here is the link to contact UK support
You can check the following links, they will show you some troubleshooting steps that can help you out
I had the same issue. However remotely or locally video was choppy and audio was great. Locally when I realized I still had the issue I reset the box (unplugged and plugged back in) and it fixed the issue. So now it seems the HD Slingbox needed to be hard reset (power on/off). Problem is it is impossible to remotely power on/off. I think slingbox needs to fix this.....
I have not tried this remotely (from home) yet. We will see. I will now unplug/plug back in the unit when I leave the house and want to use Slingbox remotely..