Alternate Caesar History

[Jona Lendering]

would another 3rd and final crack at Britain have been at the back of his mind.

I would not think so. Britain was not ready to be conquered. Typically, the Romans could occupy countries with towns (e.g., Greece), or proto-urban centers (e.g., Spain and Gaul). They ran into trouble when they had to cope with countries without logical points to attack: Britain in the first century BCE, Germany in the first century CE. Caesar, who had visited both countries, may have concluded that an attack on Egypt or the east was a better option.