Didn't last long, just resynced

Have you tried connecting a corded phone into the TEST socket and dialling 17070 then taking option 2 and listening for noise, it's called the quiet line test?

If there is no problem with the connection you shouldn't hear anything other than a voice occasionally saying "quiet line test".

Don't have a corded phone atm, will try and get one over the weekend

If noise was that constant to be audible, chances are the modem would see it and sync to a lower speed, than the 5Meg at 60dB attenuation.

Has the original poster looked for any firmware versions for the zyxel router, as it is not uncommon for different firmware versions to change how the modem behaves

In reply to a post by MrSaffron:

If noise was that constant to be audible, chances are the modem would see it and sync to a lower speed, than the 5Meg at 60dB attenuation.

Has the original poster looked for any firmware versions for the zyxel router, as it is not uncommon for different firmware versions to change how the modem behaves

I haven't managed to find any firmware for the device. I browsed the zyxel firmware FTP and there was 1 older version by the looks of it but no direct support pages for the device with useful information

The improvements I've seen over the past few days have vanished. Disconnected 5 times in the space of an hour

As far as I know, the Post Office are the only ISP that supply the Zyxel router. Like the supplier, I found it a pain in the backside. You will not be able to update the firmware as it is locked down with a Post Office custom version, which may now be compounded by the PO switching supplier to TalkTalk. I found the only answer was to purchase a decent router of my own.

May I ask which router you purchased? How easy was it to set up and were post office happy to provide settings?

Phoned them this morning, chatted to a chap about how I think it's down to the router not coping with the line length and mentioned things mentioned by you guys on here. He went to chat with his manager and they agreed it would be best to cancel the tech visit, and send out a thompson router to try first to rule out router faults all together.

Though I run a Billion 7800N now, when with the Post Office I went for one of these http://www.amazon.co.uk/TP-Link-TD-W8960N-300MBPS-Wi... It worked very well and as you see it is very well regarded at a decent price.
The PO will happily give you the Broadband connection username and password, which is a little different to the standard one you use to access your account.
The userneme is in the format [email protected] though the number is probably variable, but not to worry, Customer Services will give them to you. The username and Password are all you require to set up most routers as they usually auto-config all other settings.