Thanks for all the help & advice everyone has given - unfortunately I'm still not able to get the B525 to connect at 4G+ but my B535 connects to the same Cell ID at 4G+ everytime.
I tried following the instructions to disconnect from the network, select the network manually & reconnect (the web config pages/buttons on the B525 are different to the B900 router, but I got the idea). Unfortunately, every time I select the 3 4G network and connect the network from the router home page, it just reconnects at 4G speed).
Both my B535 (connects at 4G+) and B525 (only connects at 4G} are sat on the same window ledge approx 90cm apart from each other, both using internal antennas & with direct line-of-sight to the Three mast (approx. 100metres away). I have wondered if there could be 'interference' between them but moving the B525 to a different location in the house makes no difference except to weaken the signal between B525 & mast.
In the 18months I've had it, I've never seen my B525 connect at 4G+ speed. I had assumed this was either because the B525 doesn't support it or the Three network or my local mast didn't support it. It's only by buying the B535 I've realised that the network/mast does support it. And only through this forum that I've learnt that the B525 ought to support it.
I'm convinced the issue is the firmware that Livewire (modem.co.uk) flashed it with when I bought it from them 18months ago & requested firmware that supports Bridge Mode (which I don't use now). I have emailed Livewire several days ago for some answers or new firmware, but their support people seem to be useless & haven't bothered to reply (the sales guy is helpful & replies, so I'll have to ask him to goad the support team into a response).
The only thing I haven't tried yet is a total hard reset of the B525. If I get no response from Livewire, that's what I'll try next. If that doesn't work, I'll try the firmware update posted at the start of this thread.
Edited by smithbill (Wed 18-Dec-19 05:59:29)