FTTP Trial
FIXED
What 
There is no way you should need the PSTN line connected to the router for FTTP. You don't even need a phone line at all. You are probably still using your ADSL connection. If you were advised to do this by customer services it shows that they know nothing about the FTTP trial and should not be relied upon for any help.
What router do you have, it should have an Ethernet WAN connection that goes to the fibre ONT, the ADSL connection is not used. The router needs to be configured to use this Ethernet connection, sounds like the BT guy did a runner before setting it up properly.
@RobPN's suggestion to try a direct connection to the ONT using PPPoe is still worth doing.
edit: I've seen a later post that suggests you may not have the correct router
Judging from what you've said, ignore everything you've been told regarding FTTP over the phone so far.
Looking at your order, the engineer sent the job back in a delayed state and we've been asked to check back for further updates tomorrow 
Do plusnet have their own router/hub? The BT guy said they were all exactly the same but I take your point.
What does 'delayed state' mean? That's a new on me.
Be interesting to know what they'll advise when you check back t'morrow. As said elsewhere I think BT should call back on this pronto and get it sorted otherwise these FTTP trials of yours are going to find somebody guilty.
Bring back transportation I say! 
@Minivanman wrote:
What does 'delayed state' mean? That's a new on me.
The order is not complete and is delayed.
Engineer notes:
The service could not be provided due to Not seeing ont. This has been agreed with Control. Please see additional information Rang Dcoe and they said fibres Not working as it is not connected to the correct port in the splitter so can't see ONT needs external engineer to match up to correct port in splitter . ONT installation - COMPLETE
@Minivanman wrote:
Be interesting to know what they'll advise when you check back t'morrow.
I'm hoping they say something along the lines of The external work is complete and the circuit is now in sync. At which point I'll change the package on your account to a fibre package so you can get the fibre speeds and I'll cease the ADSL connection 
EDIT:
@RealAleMadrid wrote:
There is no way you should need the PSTN line connected to the router for FTTP. You don't even need a phone line at all. You are probably still using your ADSL connection.
Correct.
@RealAleMadrid wrote:
edit: I've seen a later post that suggests you may not have the correct router
Although it's correct we hadn't sent a Hub One, reading previous posts seem to suggest the engineer left a BT Home Hub which should work the same but would just need some manual set up with the Auth details.
It's not ideal when routers aren't sent out on FTTP, however the vast majority of FTTP orders are not linked to the ADSL and we'd generally be able to leave the ADSL in place until we see the connection on the account connecting through the FTTP BBEU.
Judging from what you've said, ignore everything you've been told regarding FTTP over the phone so far
@Minivanman That's the best advice I've seen so far
Let the PlusNet help team sort it out via this thread and tickets on your account, forget about the normal support centre , they won't know about FTTP.
It sounds like @HarryB has it in hand.
As regards the BT hub, the hardware IS the same as the PN one (well if it's a HH5a anyway!) but the firmware is different. As Harry says the PN will autoconfigure to your login details whereas the BT one will need manual configuration for your username/password at least. However, seeing as you now appear to be connected via it for ADSL you must have done that correctly. When the FTTP goes live, it (the router) MAY auto detect the FTTP connection or you may have to manually configure it to do so.
@Minivanman wrote:
I was hoping to keep the ADSL connected Harry just in case we have power cut and we need the telephone line?
I wouldn't cease your phone line. Just the broadband that's provided on it.
@MisterW wrote:
However, seeing as you now appear to be connected via it for ADSL you must have done that correctly. When the FTTP goes live, it (the router) MAY auto detect the FTTP connection or you may have to manually configure it to do so.
The auth details would be the same for the FTTP connection as they are for the ADSL (username@plusdsl.net and the password)
It would just need moving across to the ONT instead of the phone line.
Hopefully @Minivanman won't be waiting long for the Hub One anyway as they're sent out via first class post.
The good news is that our suppliers have advised that the external work has been completed.
The less than ideal news is that they've requested we book an appointment to complete the internal work...
Given the previous notes on the order, I'm lead to believe that the internal work is already complete, so ideally I'd prefer to avoid booking another appointment if possible.
Could you try connecting up to the ONT on port number 1 and let us know if you can get online using this now (Please note, the speeds will still likely be ADSL speeds at this point)
If you're still having problems getting online, I'll happily get another appointment booked, but hopefully it's working and I'll request they just close the order as complete
Further to my previous post Harry, have checked this morning and it's already connected to the ONT on port number 1 so....
As regards to the installation itself - and I hope somebody your end will take note of this, I am not at all a happy bunny at the way it's been done. Where the fibre cable goes into the ONT it is short of the box which means the cable sleeve is not secure and all that is holding the cable to the box are those ultra thin fibres - so could this be the problem? The BT guys yesterday did not bother to look and I have only now noticed it because of checking as suggested on that port number 1. Add to this the cable goes through a plasterboard wall and no grommet has been fitted which leaves a rather messy hole as you can imagine (I used to fit this for a neat job when running Sky CT100 cables). Where the cable runs from the outside it's such a tight run that there is no drip loop on the cable which means of course that when it rains water is going to run down the wall, along the cable and into the house - and am I being over fussy in saying he's used black clips to secure a white cable? I hope not.
Your plusnet hub arrived this morning so don't know whether or not to fit this or leave the BT one in situ until it's all up and running and it would of course mean I will have to re-enter all those codes to the computer and all the rest of my wifi stuff in the house but that's no big deal as long as it works.
All in all not a professional job by BT turning up as they three times unannounced, doing a shabby job, fitting the wrong hub, leaving me to off line with no phone or internet and having to figure out with plusnet's help how to get it half working by plugging a fancy fibre hub into the PSTN socket!
If it ain't broke don't fix it eh?
If only 
I have done as you suggested Rob and it does work so thanks - I am connected direct to it now and not via the hub and the PSTN line as advised to do by plusnet's phone advice.
Where this leaves me now I have no idea and although the speed is still below 5mbps (have been told it takes a while to settle in) it is working via the new fibre cable despite it being a rather shabby install.
Over to you plusnet
@Minivanman wrote:
I have done as you suggested Rob and it does work so thanks - I am connected direct to it now and not via the hub and the PSTN line as advised to do by plusnet's phone advice.
Glad you've finally taken the plunge and established the connection is working, so that's good.
HarryB did say earlier in the thread to disregard the phone advice, which as others have alluded to was a load of tosh!
@Minivanman wrote:
Where this leaves me now I have no idea and although the speed is still below 5mbps (have been told it takes a while to settle in) it is working via the new fibre cable despite it being a rather shabby install.
So you now need to introduce a router back into the setup. I'm not familiar with either of the 2 routers you've mentioned but it shouldn't be too difficult.
As mentioned by @MisterW the BT supplied one will need configuring with your PN credentials, whilst the PN supplied one will probably either be already set up with them or will obtain them automatically.
As you have been connecting via your old ADSL it would probably be a good idea to disable that in order not to confuse yourself. 
Edit: PS, the FTTP does not need any time to 'settle down', the fact that you are seeing your old download speed is because PN have not yet switched the account over. You will probably find your upload is already running at the new speed - either 2Mb/s or 20Mb/s depending on whether you chose the 40/2 or 80/20 package.