The letter, which has also gone to the archbishops of Westminster, Vincent Nichols, and Birmingham, Bernard Longley, and the Charity Commission claims that key management decisions - including "the incurring of substantial expenditure" - are being made in the diocese without proper consideration and approval by its board of trustees.
The four signatories of the letter, all lay Catholics, were among five trustees - including a priest - sacked earlier this year after they voted against a proposal to make three members of diocesan staff redundant, and voiced concerns about the way the diocese was being governed.