If you do not want the fan to come on with the light, and it is to be a timer fan, you will either need a pullcord (or a single pole switch either outside the zones or outside the room) to trigger the fan to come on in addition to the TP isolator, or else you can use a PIR to trigger the fan.
If you have a live feed already picked up off a suitable (5 or 6A) circuit, and it is convenient, you can piggy-back off this for the fan.
If you have room for the terminations and it is convenient, take the T&E feed into the SP switch triggering the fan, terminate the live feed to the common along with the live out of a three core. Join the neutral of the T&E with the neutral of the three core in a separate connector. Connect the switchwire of the three core to L1. Connect the CPC's through.
This three core then feeds the TP switch, the other side of which connects to the fan. Thus, the SP switch triggers the fan to come on. When the SP switch is turned off, the fan continues to run courtesy of the permanent live feed. For maintenance, use the TP switch to isolate because the SP switch will only isolate the switched live, not the permanent live.
If the manufacturers instructions insist on fusing down, put an FCU in with a 3A fuse in right at the start of the circuit (where you piggy-back the feed for the fan from), but there's no need, unless you want to put a switched FCU in, then you can do away with the need for the TP isolator as the DP isolator will isolate both the live and switched live as the fan has its own "on/off" switch.
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