What is a Chartered Scientist/Engineer & how do you become one?
I'm basing my answer on Ireland, where my Brother became a Chartered Engineer. 

In relation to the points of your question.


Normally in Ireland you obtain a Bachelors (Hon) degree (up to 2012 now a masters degree) and can become an Associate member of the Engineer Institute. After a period of time, or either further study or in the workplace you may apply to become a Chartered Engineer Regulations here. I know in my brothers case for his application he had to write up any course he took after becoming a member and also any details of any project that he worked on.
It appears a masters degree is needed now but a Bachelors (Hon) degree awarded up to 2012 will be accepted up to 2020. Page 7 of the regulations linked above have details of progression routes available.
There are a number of accords that ensure cross-border recognition of the qualification. Again as an example, my Brother was able to secure a Engineering Job with a European multinational Engineering firm in the UAE within about 6-8 weeks of moving there.


It is possible that the Irish and British systems are similar due to the historical link between the two countries. Unfortunately as per your question I have no information on the term Chartered Scientist.