Is there any reason you are switching the router off overnight? ADSL is designed to be an "always on" connection.
There are really no advantages and several disadvantages to switching the router off overnight unless you are experiencing a loss of sync in the evenings and are rebooting in the morning in order to get a higher speed.
As you are in the UK, it wouldn't be a huge leap of faith to assume that you obtain your internet connection via BT Wholesale, even if BT are not your ISP. (As you don't have a HomeHub I'm assuming that they are not) BT's network requires a stable sync of at least 3 days before it will stabilise your IP profile (which dictates your speed) in the event of a higher sync speed being obtained. Worse still, if you have ever had several loss of sync events in a short space of time, the DSLAM may well have raised your target SNR, which requires a stable connection for at least 14 days before returning to normal.
In other words, by switching it off overnight, your speeds can only go down.