How hard is it to replace this please? 

https://www.ebay.co.uk/itm/302548549064

Are you replacing this tail pipe because the hanger bracket/rod bit has become detached?

If so there is an easy fix.

ScaniaPBman.

Hi, yes it has rusted through

Ah well, just get a big jubilee clamp which will fit over the pipe AND the rod and screw it up clamping the rod tightly to the pipe and pointing the rod in the correct direction for the rubber hanger. I have done this on two tail pipes so far with complete success. They have lasted 2 years so far.

As a finishing touch I plastered everything in the clamp area with high melting point grease. I felt better after doing this bit but I am not sure it made much difference really.

ScaniaPBman.

Does that pipe just get clamped onto the exit of the silencer?

I don't know, have a look underneath the car. 

From experience the joints in replacement exhaust parts do not always exist on the original exhausts. When I bought a replacement rear silencer for my 2007 fiesta (original rusted through) there was no joint ahead of the rear silencer on the original exhaust. I had to saw off the original silencer making sure I sawed in exactly the right place. I recall the same occurring on a Ford Escort I had years ago. 

You need to cut through the old tailpipe Infront of the anck box and then clamp the new one onto the existing pipework using a clamp.. but due to lack of room it's not easiest of jobs, more fiddly than owt else. Ineeded to do mine n ended up changing the back box as was easier to cut from centre box n remove back box and tail pipe. 

Its not as bad it would seem I've replaced our MK1 focus estate and had to as @Dave1981 mentioned refit the backbox due to it being from a diesel which didn't have 1 on and as @ScaniaPBman said ours is held up by jubilee clips ( heavy duty type ) it's a  scorpion 3" and not made for a ford..