Connecting new 110mm waste to existing run

[vala]

My builder has come to the point of making the connection between a new waste run into the existing sewer run.
He plans on using a plastic 3 socket 90° tee with flexi couplers.
However after a conversation with Anglian water's drainage department today he's been told that he needs to use a clay y branch, then a 45° piece before connecting up to the new pipe run.
Has anyone ever heard of this?
In particular using a clay y branch and 45°?
He's a bit puzzled as to why this is the case and is going back and forth with their technical department to get clarification.
This is slowing down the build so thought I seek opinions and experience from here.
Thanks

 

[denso13]

Has anyone ever heard of this?
In particular using a clay y branch and 45°?

The ones I have done were just that. If it's a public sewer then Anglian have the final say unfortunately.

This is slowing down the build so thought I seek opinions and experience from here.

It's just as easy with clay and flexi couplings, no need to slow anything down.