If your modem stays connected but your router disconnects, the problem is likely to be either a faulty modem or dodgy cable between router and modem.
Yes replaced both, doesn't help so put the old router back, as a much better router. Nobody seems to have any idea when I ring technical help lines, so guess I will have to wait for an engineer to come out and have a look. At least it is only intermittent, and usually in the morning? Many ,many thanks for your help