If there is anyone who is, or has been, involved in exam setting or marking, Id very much appreciate some help.

I have had students taking exams at B2 and C1. In all cases writing a letter or email has been a requirement. Often this is a business to business, or inter-business communication.

The reason they find this daunting is not due to failings in their English, but their lack of formal business communication writing skills.

They would certainly struggle, and in most cases fail, to complete the task to a satisfactory business level, in their own language.

My question is, how much might they be penalised for a lack of business knowledge and experience?

I had one student who produced a 300-word email that had two very minor English grammatical errors. But the letter would hopefully never be sent within a professional environment.

To be fair it would help if the hypothetical requirement (described in the exam question) was realistic. As they are often not realistic, am I right to think that the English grammar and spelling leads to 90%+ of the marks?