As it happened I was awake, monitoring the river 80metres from our house which, in places, had breached it's banks. I also received the floodline alert email. Unfortunately none if my 3 phones actually rang but, on dialling 1471 the following morning, the automated voice told me I'd been called! We had full fibre VOIP installed 10 days ago.
Rang my house phone's with moby, they all rang.
Have contacted BT tech' & it's being investigated, will also notify floodline.