Regulation 526.5 requires all joints to be inside a suitable enclosure or accessory and 526.8 requires all unsheathed conductors to be inside an enclosure, i.e. No exposed unsheathed wiring visible outside of a junction box or accessory. The use of Wago's and or any use of insulation tape does not remove these requirements. Whatever method you choose you also must have a means of securing the cables so they cannot be pulled outside of the enclosure or so the joints cannot be pulled apart. A box with appropriate cable clamps does not need to be screwed to a beam, i.e. this is no different to a plug or socket on an extension lead, as long as the cable clamps are tight, no live unsheathed cables can become exposed. (Whereas a traditional round j/box, screwed to a beam and with all cables clipped, would not need cable clamps as both box and cables are fixed to prevent movement of the joint.)
Doc H.