"No privilege attaches to communications between solicitor and client as against persons sharing a joint interest with the client in the subject-matter of the communication, e.g. as between partners; a company and its shareholders; trustee and cestui que trust; lord and tenants of a manor as to customs of manor; a lessor and lessee as to production of the lease; reversioner and tenant for life as to common title; two persons stating a case for their joint benefit; or a husband and wife who are not genuinely, but collusively, in contest. Nor does any privilege attach as between joint claimants under the same client - e.g. between claimants under a testator as to communications between the latter and his solicitor. Thus where two persons agree to divide the profits made by one of them on contracts made with third parties, the person who does not make the contracts is entitled to production from the person who does of, for example, the opinions of counsel relating to litigation between the contractor and a third party. But where the communications relate to matters outside the joint interest, they are privileged even as against a person bearing the expense of the communications - e.g. communications between a plaintiff corporation and its solicitors, against a defendant ratepayer as to matters not connected with rates; or between a company and its solicitors consisting of confidential advice to the former in an action against a shareholder; or between a trustee and his solicitor as against the cestui que trust, where the communication is not made for the former's guidance in the trust, but to enable him to resist litigation by the latter; or where it concerns his character, not as trustee, but as mortgagee of the client. Though the privilege does not protect one person with a joint interest from disclosing to the other matters which are the subject of that interest, both parties are entitled to maintain the privilege against the rest of the world. But the rest of the world for these purposes does not include the trustee in bankruptcy of one of the parties, or his successor in title. In case of joint interest, it is sufficient, as against third persons, if one only of the interested parties claims the privilege, though all must concur in waiving it. A joint interest for these purposes is not a rigidly defined concept. It is apparent that those categories described above, such as partners and the like, come within these principles. But a mere common interest in that outcome of litigation will be sufficient to enable any party with that interest to rely on it."