Hi and Welcome to the boards.

Weather can play a factor sometimes with the satellite signal, also anything blocking the dish can cause this issue too, sometimes it can be BSkyB's fault, if you're getting this constantly it's probably worth giving them a call.

Before ringing:

Consider unplugging the digibox and leave unplugged for 10 minutes then plug back in and turn on.

Check all the connections to the back of the box are secure and not loose. As the same for your TV, scart leads can be a pain for coming out, especially if the lead has no slack and the TV or digibox is moved (i.e. when dusting).

From your remote with the TV switched on and your Sky channel or input. Press services button then Option 4 then options go into each option and run the tests for 6,7,8.

If none of the above resolve the issue call Sky, but tell the agent of what you have done.