Many thanks for the replies and very useful info... I'll certainly keep it in mind if problems do start to crop up and it looks like it's a double NAT issue.
I think if the SH had not powered off all the other LAN ports when switching to modem only mode, I'd have most likely stuck with that but given the location of my SH and the other gear (in other rooms), it would have meant running a number of different cables through walls just to get a LAN connection to the likes of my Sky box, which is sitting no more than a matter of inches from the SH!
My first hookup when I got VM cable broadband was to follow the good advice from this forum and switched it to modem mode and although again, things worked fine connecting to the TP-Link switch, I then had the problem of the LAN ports on the SH being switched off and getting my Sky box a connection so really, I guess I ended up with a happy accident being able to run the SH and the TP-Link router in a double NAT situation.
My guess is that I'd most likely start to run into problems if I wanted to do port forwarding or something like Skype?.... but at the moment at least, I don't need that sort of functionality and again I have to say that for me, the TP-Link router works great alongside the SH
Cheers!