IP Camera suddenly stopped transmitting outside of the network
Couple of issues here.  


  I bought the camera for about £15


Most likely, this is your problem.  I spent a few minutes perusing the IP cameras on Amazon, and £15 is the bottom, bottom, bottom of the barrel.  This thing is simply too cheap to have any expectation of reliability.  

The wisdom of scraping the bottom of the barrel is arguable. What's not arguable is that it's definitely not worth sinking your precious time into troubleshooting it.  The normal expectation is that when it breaks, you throw it out and buy another one.  Once you are sick of this merry go round, you buy a better one. 


  The internal port is 192.168.0.42:80 I have forwarded this port to [external ip]:80 


OK, so you exposed the camera to the public internet.  I'm really not sure why, the camera should be initiating contact with AngelCam, and that should work  just fine through a NAT/router; there's no reason or need for Angelcam to initiate contact with the camera so no reason for the camera to be publicly exposed.  

Anyway, by leaving it publicly exposed, someone scanning IP addresses (note your public IP is IPv4, which makes it easy to scan) probably found your camera, threw the usual exploits at it, found a vulnerability, and either own your camera, or accidentally broke it by their cracking.  Because manufacturers of $15 cameras don't issue patches, even if you were faithful in patching.  

(By the way, this is how small businesses go bankrupt.  Some silly thing like this is overlooked in their PCI-DSS self-inspect, it gets used as a gateway to hack a credit card machine, etc...) 

In the future, don't forward public ports for security cameras.  Get cameras smart enough not to need that.