Thanks for the reply. I tried a different IP address, did a couple of reboots and now I have some measure of success. Doing this the button now can access my test web server on EC2, however it still refuses to access AWS's API gateway in order to fire a lambda - which was what I got the button for in the first place.
As a stop gap I've nocked up a quick python web server on my test machine that has the same functionality as the lambda. I was hoping to use the lambda so I would not have to run a server, however its now working OK on a tiny cheap AWS t3.nano instance. If I get motivated I'll try to dig in more as to why its not calling the API gateway URLs. A problem for another day I think.
I've no idea why changing the IP address did anything, neither the old not the new IP address were in use, nor was there a clash with DHCP (I have it set to only use IPs from 192.168.1.100 onwards, 192.168.1.14 didn't work but 192.168.1.40 did.)
Thanks again