Plastic to clay downpipe

[StudWall]

Decided to do a bit of weekend renovating of my guttering since it's old and rusty and flaking paint.

I've managed to remove the old cast iron downpipe and detach it from the underground connection which appears to be an elbow of sorts. The old pipe was just mortared in place but the downpipe doesn't seem to match the size of the underground pipe (of course)

I've got some 'standard' 68mm downpipe but I can't seem to find an adapter to join them properly.
The bigger section of the underground pipe seems to measure about 120mm and the inner about 80mm.

What is the correct way to finish this off properly?

Cheers

 

[Bosswhite]

I would wrap plumbers hemp around down pipe to fill gap then cement the joint .

 

[CBW]

One of these might work: https://www.screwfix.com/p/floplast...JU5v6ynaywCOmqAdRAhoC8KAQAvD_BwE&gclsrc=aw.ds