No need whatsoever for a solicitor at this stage, although now you mention it, it would be interesting to submit an application to CrewDefence for formal legal advice on the matter.
The legislation is crystal clear on this matter; branches MUST release accounting information to members of their affiliated Union within 28 days of a request to do so by a member of that Union.
End of.
Trade Union and Labour Relations (Consolidation) Act 1992