No - replace the twin and earth for 3 core and earth.Permenant live to L,
switched live to SL and neutral to N are some common terminal identifiers
Sarah
Unfortunately you need a neutral as well as a live to make the light work so unless you are lucky and there is a neutral at the switch you will have to find a neutral from the same lighting circuit from somewhere else
Sarah
Or crimp each wire with through crimps as these will take up less room than connectors but you would need to use the ratchet style crimpers rather than the horrible 'manual ones'!
Do not connect those lights to that circuit.The earth is as you are probably aware there for safety and needs to be connected.An electric shock is a possibility if a metal fitting requiring an earth is connected up without one if a fault were to occur
Sarah
If the immersion heater is on its own circuit, is a standard 3kw type and you are sure it is the switch at fault then you will need a 20amp double pole switch with a flexible cable outlet.It is up to you wether or not you would like a neon on it but it does help you see at a quick glance if it...
All the clues lead to the fact there could be a loose connection in the landing ceiling rose (or possible damage to cable between landing and rest of circuit) This assumes that the landing light is the first on the circuit from the symptoms you have given.
As others have said if nothing is...
I would agree Lectrician that the easiest way is to take the lighting feed to the switch, join the neutrals together in a connector, earths together in the terminal at the back of the pattress and obviously switch the lives