Ashley part of Hager do a Maintenance Free Junction Box which you can plaster over but normal one with screws have to be accessible. For lights 5 amp is ample.
Advert shows it as 4 way with 4 connections. The other way is crimp or solder with self alginateing tape then standard insulation tape.
I would visit a whole sale outlet and ask new things every week and they are normally helpfull.
If the cable is being extended and you can put the existing cable under the floor then get a 4terminal 20 amp junction box and connect the wire into this and put the junction boxin the floor if this is upstairs.
all the best
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