I presume that where you have mounted the new extractor renders the existing cable too short (hence the need for a junction box) which would be perfectly acceptable providing the existing cpc is maintained into the fan assembly (which of course will not used but should still have earth continuity within the cable) and confirmed during testing/certification.
You mention running a new cable to the light? which would indicate no isolator. I would recommend installing an isolator switch whilst upgrading the fan.
The junction box actually has 4 ports for cables 4xL1 4xL2 etc. This allows for various termination scenarios and not just a straight cable one in one out junction.
Yes this is correct. Currently the cable runs from bathroom light ceiling to extractor fan. The new inline Manrose extractor fan is in the loft. So a new cable run required from existing cable feeding the current extractor fan to new fan in loft using 3 core and earth cable via a terminal box is what the electrician advised.
There no earth in the wires feeding into the ceiling light so not sure why the previous electrican took this out. Would there be a valid reason why this earth might be taken out? We have had no issues with it so far.
The hager 4 terminal box - the 3 core and earth has bare earth cable - as this won't be used it can be stripped and terminated in the 2nd port of L2 ? or left as is ?