Thanks for checking in! I still couldn't connect to 5G - but I think what's actually happened is I've been confused by my iPhone 5G symbol....How did it go?
From a bit of googling I don't actually think my iPhone is connecting to 5G and that instead it is connecting to a '5G ready mast' - when I go into the hidden settings menu on my phone it says its using cellular band 3 - which isn't an assosciated 5G band so I think what I'm really getting is LTE+.
I don't think there's any fault with the router and I'm still getting speeds of around 200mbs which is still a big step up from the 30mbs I get on my FTTC connection (over a mile of copper to the house!) - thinking of investing in an external antenna so I can move the router into a more permanent spot as the windowsill I get the best signal doesn't have power anywhere near!