When my wife had a second line installed for her work, Openreach used this cylindrical plastic contraption.
I imagine it uses screw terminals instead/as well as IDC, because of the mixture of wire types.
The 2pr from the pole enters on the RHS the "new line" (long since disconnected) is the lower cable, and the existing CCS "figure eight" is the one still in use, it's only a couple of metres long until it gets to the linebox in the house, but is well past its sell-by date, although gives no trouble.
When I moved into this house in the mid '70s one of my first DIY jobs was to remove two runs of unsightly cable on the front of the house that served a bedroom phone extension.
The cable turned out to be lead-sheathed twin, that looked a bit like modern 1mm or 1.5mm twin & earth mains cable.