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They look like jelly crimps, they create a connection that will also keep out moisture.
You can use a junction box with screw down terminals to rejoin the single pair(s). BT/Openreach would normally use one with IDC terminals that you would need a krone/punch down tool to fit but screw down will work just fine and you won't need special tools.
If you're ever given any grief, just say it was like that when you moved in.
Great! wasn't sure if there was some kind of voodoo magic in those clips.