Joining two 10mm twin and earth cables
I've never seen a qualified electrician leave twisted and taped up wires in 30 years on the job. And that is because it is a ridiculous way to form a connection. The tape will degrade over time and turn into a sticky mess. Put the connection into a proper junction box rated for the job, they cost pennies.

p.s. I could nearly live with it, if the wires were soldered and then the whole thing put into a box, but even then the tape won't last forever.