Ugh, well got the new router, got it up and running with a few PCs, and it didn't make any difference
I've now spotted that I don't have Perforce service running on the server, assumed Helix was enough but apparently not when compared to dev PC
Fed up with this now - it stopped working after BT guy swapped out the router, and I must have spent over 6 hours trying to get it working again. Hate networking stuff, going to have to take a break for a few days - I just want to get back to the actual work, but I can't, so everything's on hold.