Is it illegal for a partner in joint business to get private email?

Alasdair Taylor's answer to Is it illegal for a partner in joint business to get private email? (1845704850)

There's no general prohibition in English law on a partner operating a private email account.

Your question does however raise other questions. Particularly, what is the account being used for?

A partner has fiduciary duties to the other partners.  See:

http://www.slatergordon.co.uk/partnerships/duties-of-partners-to-each-ot...

Also, a partner could be under a contractual duty to disclosure defined categories of information to the other partners.

I suspect that there is more to the situation that your short question communicates.