I can assure you that BT do not routinely do repairs/upgrades during the night, there is no need to do so.
At a time when the drop-outs are occuring, lift your phone and dial a digit to break dial tone. Listen for any noise.
If nothing heard, dial 151 and follow the prompts to test your line. If all clear, follow the prompts again to report a fault, intermittent noise at night. BT will be obliged to carry out a more extensive test.
If still no solution, ask Eclipse to raise a broadband fault with BT (only your ISP can do this).
Finally, I doubt whether changing ISP would resolve your problem.