I had a similar problem. I have BT fibre to cabinet but have recently noticed increasing noise on the landline; then I found I was getting broadband disconnections if my landline rang. My main socket (which was already installed when I moved in to a new-build apartment) is the BT/Openreach NTE 5C socket with the (then) standard single outlet. I have been using it with a filter to my Smart Hub 2, with a filter also installed on the 'phone extension to my landline cordless base station. This is the recommended set-up, but I think that the house wiring on the landline at the socket itself can still cause interference.
For me the solution was to replace the original faceplate on the main socket with a Mk 4 faceplate; the Mk 4 has one phone and one broadband outlet, and both are filtered internally before the outlets. This is a very cheap and easy fix if you already have the NTE 5C socket. The faceplate is only held in place by clips and released by pressing on the two sides - the faceplate plugs into the plate behind it; there's no wiring involved. You can buy a new NTE 5C socket with the Mark 4 faceplate (the faceplate's not available as a separate item), and all you need to do is remove the old faceplate from your existing socket and replace it with the Mk 4 faceplate. You are left with the additional components from the new socket bits that are identical to those in your existing socket, but as the whole new unit is only £11.99 from Amazon it's not a big deal.
This eliminates the need for additional in-line filters on both your broadband and phone line; since installing mine I've had no broadband outages and I have a much quieter landline - and as the swap doesn't involve any interference with the socket wiring there's no requirement to call out (and pay for) an engineer.
Two points to note:
1. The outlet for the 'phone is a BT phone type, and for the broadband is RJ11, so you will need a suitable lead to connect to your hub if that's not what you have already.
2. The 'phone outlet on the faceplate and any home landline sockets will not be suitable for broadband - i.e. you won't be able to plug your hub into a phone extension socket.
NTE 5C Test socket check
