@klipse

Thank you Klipse, the links I find from your suggestion are very helpful.  It seems that Sky staff are at odds over this one.  When I looked into taking on Sky, (a black day in our household), using my own router was a big deal for me and I asked whether this was supported specifically.  I was told "yes, you can do that!".  Then when I had a tech query over something else, as an aside I wanted to confirm with the tech support operator that it was ok and the answer was "definitely not!".  I pointed out to him that I had been told it would be ok when I enrolled and he just said "she shouldn't have told you that".

As I said, I have managed to get my Sky login details via Wireshark if they turn out to be needed, it's the other necessary pieces of info I'm not too sure of.  Some links say the login details are necessary and some say you don't need them, just use generic info.  I've got nothing to lose but a bit of time by trying to just replace the Sky router with the A7 and see how far I get.  I'll report back with what I find.

Thanks again.

  @Bordonbert I've spent a little time now trying various options here without success.  Simnply replacing the Sky router with the Archer A7 into the WAN port did not work.  I followed a YT vid where a guy set up a TP-Link AC2100 router through the "Quick Setup" process.  I assumed they would be similar but it appears his is more advanced as I didn't get the same options as him!  His second step is to "Select Internet Service Provider (ISP)" where he chooses "SKY(MER)_VDSL".  In my case that step is named "Internet Connection Type" and only offers me Dynamic IP, Static IP, PPoE, L2TP and PPTP.  Auto Detect selects PPoE.  Next I enter the authentication for Sky which is correct for my setup rather than the generic 1234abcd version often recommended.  Then Wireless setup and Summary then Save and it cannot connect.

Following the Advanced route leads me to a setup page where I can enter similar info but it requires a setting "VPN Server IP/Domain Name" which has foxed me.  It will not progress beyond that without the entry and it requires something in a particular format as it errors on that point.  Can anyone shed any light on that?

I have even tried using both routers and trying to disable DHCP and wireless on the Sky router.  It won't allow it.  DHCP is irrevocably enabled by default.  So no go there either.  I'm beginning to think that somehow my AC1750 is a non-starter even though people report having done this..

  @Bordonbert Yes, in that good old embarrassing way, as soon as I had posted that and knew what I was looking for I found the IPv6 area.  I was totally unaware up to that point that I could turn off IPv6.  It's on now and functioning, but it still doesn't get me logged into Sky internet.  I'm really beginning to think that there is something odd about my own router.  It doesn't seem to have the options that some others do even though I have now performed a manual update of the firmware to the latest version downloaded directly from the TP-Link site.

  @Bordonbert 

If I am understanding this right, there should be two ways to connect a 3rd-party router to Sky FTTP.

1) Using the "Sky MER" option (also called DHCP option 61), which is not supported by regular TP-Link wireless routers like the Archer A7. (at TP-Link only their ADSL/VDSL routers have it)

2) Connecting via IPv6. (provided IPv6 is already supported in your area)
>> Try to replicate all the settings circled in red in the two screenshots below.

By the way, in case this Archer A7 is not a new device and you have already adjusted a plethora of settings on it over time, then it may be a good idea to restore the router to factory default settings first, in order to have a "clean" starting point.