Update: I installed UE4 (build 4.7.3) onto my work computer and it worked just fine. The first time I ran the lighting build it told me a firewall was blocking swarm and if I wanted to allow it through the firewall. After allowing it through it built the lighting and didn’t prompt me again after that.
Previously, I had temporarily disabled my firewall on my home computer to see if it that would fix the problem but it didn’t work. However, I’m pretty sure this is a firewall problem and I probably missed something last time.
I’ll have another look at it tonight and post my results.
Thanks for reading