You just jogged my memory…as well as loading the UK locale file, I also loaded the English UK language file. When I did that, I also moved the US English language file into the disabled languages. It appears that this is what caused the problem.
I have moved the US English language file back into the the “Enabled Languages” and it all seems to be working again.
Sorry to have troubled you … hopefully I won’t have to bother you again. Once I have got my head around SuiteCRM a bit more I will have a look at implementing a fix to stop a ‘critical’ language being able to be disabled.
Many thanks
Simon