When I make or receive a call my broadband drops

[#1]

Hi
I've noticed recently that when I'm on the phone, my broadband drops (I thought it might be just the wifi, but having just had it happen, I checked what router says, and it's been connected for a couple of minutes)
I also had a strange fault on my phone line the other week, which mysteriously corrected itself after I'd booked a BT engineer. (I cancelled the engineer so as not to get charged)
Any ideas?
John

[#2]

Possibly a dead filter or two?

[#3]

Can you try a quick test.
Disconnect the phone from the line then ring your number from a mobile and see if the broadband drops or the noise margin dips or there are a lot of errors reported by the router

[#4]

someone had unplugged the phone from the filter, and plugged it straight into the socket.