well the fan is now wired with 3 core+e the terminals in the fan are:-
L,N,LT,Lh,LL. i have black cable from LT going to L1 in the pull switch, the brown is in L on the fan, blue is in N on the fan., a link is in place from LT to LL for the slow speed as per instructions! from the fan i have black in L1 on the pull switch, from the light (rose) i have three core now. black from three 3 core into comm on the switch, brown from rose linked to brown from the fan. neutral from the rose linked to neutral from the fan earths are linked in the pull switch terminal.
I'm finding it hard to understand how you've tried to wire this. However, from what you've said, the best I can make out so far is this:
[code:1]
Fan: Switch: Rose:
L------[brown]-----O------[brown]----- BROWN?
N------[blue]------O------[blue]------ NEUTRAL?
---LT-----[black]---L1/COM---[black]----- ?
| LH
---LL
Earthing omitted for clarity
[/code:1]
First thing of note is that, unless you've used blue sleeving, the colours in your wire sound a bit odd. Are you using 4-core flex or something?
Second, it would seem very odd that the manufacturer's instructions recommend linking LT and LL to control the speed. If that's the case, what happens when the LT terminal doesn't have any voltage applied? The fan would most likely not run, meaning the timer run-on wouldn't work either.
So, firstly, I think you should remove the link between LT and LL, and instead,
link the LL and L terminals.
Secondly, you need to look at the wiring between the rose and the switch. You don't seem to mention what happens with the black wire along the entire length of its run, but it's irrelevant, as you only need 3 core + earth between the switch and fan and not between the switch and rose.
As you've already changed all the wiring to 3c+e, I'd suggest you completely disconnect the black at both the rose and switch. Pick up a permanent live at the rose on the brown, and neutral on the blue. [Not to teach you to suck eggs, but the brown flex to the lampholder is NOT permanent live, so this isn't just necessarily a case of finding another brown wire and linking to it.]
At the switch, link both blue wires together in a terminal block, such that the neutral wiring is continuous right the way from the rose until it reaches the N terminal on the fan.
Brown (permanent live) from the ceiling rose should go to the COM terminal on the switch. Also in the COM terminal should be the brown wire from the L terminal of the fan.
Black from the fan's LT terminal should go to L1 on the switch, and should be marked with brown tape or sleeving at both ends to indicate the presence of a switched live.
All earth wires should be sleeved green/yellow, assuming you aren't using flex, and then be continuous throughout the run between the ceiling rose and fan. If there is an earth terminal at the switch, they should also be connected there. As the earth connection doesn't appear to be necessary for the fan itself, you should safely isolate it in an extra terminal block or similar
at the fan.
If you follow the above instructions, the fan should run when the switch is on, and then continue to run for the preset timed period after the switch has been turned off.
As has already been pointed out, this is notifiable work on account of being in a bathroom.