I'm about to replace an old timer bathroom extractor fan with a modern one. The old one is fed by a three core and earth cable, the third (yellow) core presumably being the connection to the pull cord switch. I haven't yet been into the loft to check exactly how the wiring was installed.

However, the instructions tell me that the new fan (and light according to the circuit diagram provided) need to be fed via a switched spur with a 3 amp fuse. Double pole switch or plug and socket should be located outside bathroom.

I doubt that the existing installation is via a switched spur (circa 1968), so presumably I need to install a junction box in the loft space to carry the lighting circuit, feed the switched spur from that and then the bathroom light rose from the spur.

The fan presumably is fed with constant live via the ceiling rose with the 3rd core connected to the return terminal from the pull cord switch.

Please confirm and explain what is a double pole switch as opposed to any other.