It might be worth delving into the "Technical Menu" (or similar) on your STB. On my bit of kit I can then access "Auto Service Update" and "Software Download" menus, with the option to turn either ON or OFF.
You may also know that at present UK digital terrestrial transmitters are operating on reduced power (to mitigate interference with analogue). We are told that when a region's analogue transmitter is finally switched off, the power of the corresponding digital transmitter will be increased. So hopefully digital reception will improve.