I will second (or third/forth/fifth!) how great Wago connectors are, they are pretty much the electricians standard cable joining connector here in the UK from what I've seen online, much easier that using standard "choc-bloc" terminal strip, Wago also do special enclosures for them (for just housing the Wago connectors/wiring) to make it maintence-free for installation work.
The lever type already mentioned will take conductors from 0.5mm-6.0mm! both stranded and solid, I've used them happily on 0.75mm² rubber pond flex, 1.25mm² PVC flex and 2.5mm² solid T+E.
Specs here:
https://www.wago.com/gb/installation-terminal-blocks-and-connectors/compact-splicing-connector/p/221-613Another option I have used for when I needed to connect multiple cables together and didn't mind if the connection was not as easy to remove is to use a combination of standard "choc-bloc" terminal strip and insulated bootlace ferrules designed for two cables, you can connect 4 cables together easily, safely and reliably this way (bootlace ferrules being the bomb for wiring plugs and such like with stranded cable, and are mandated on all new devices in the UK with a rewireable plug).
(choc-bloc referring to this type of terminal strip in the UK
https://i.ebayimg.com/images/g/w0IAAOSwA3dYVqZn/s-l300.jpg )