A worker has the right not to be subject to any detriment by any act, or deliberate failure to act, of their employer on the grounds that they have made a ‘protected disclosure’ (section 47B Employment Rights Act 1996).
In order to constitute a protected disclosure, a disclosure to an employer must be made in the reasonable belief that it is in the public interest and that it is of information showing one or more of a number of matters listed in section 43B Employment Rights Act 1996, including:
That a person has failed, is failing or is likely to fail to comply with any legal obligation to which they are subject;
That a criminal offence has been committed, is being committed or is likely to be committed;
That the health and safety of an individual has been or is likely to be endangered.
Whether a disclosure was made in the reasonable belief that it is in the public interest is a two-stage test. First, you must consider whether the worker making the disclosure genuinely believed it to be in the public interest. If it is determined that the worker genuinely held that belief then you move on to assess whether that belief was reasonable.
Protected disclosures may be made to someone other than an employer, such as regulatory bodies, the media and prescribed persons. The criteria which must be met for a disclosure to be afforded protected status varies depending upon the nature of the recipient.
It may be that the Solicitor has a claim. I understand that your husband is a service provider and not an employee and terfore was commissioned to provide the report. If so, then the employee rules may not apply.
The following law firm may be able to offer some further guidance: https://constantinecannon.com/practice/whistleblower/contact/london/?gclid=Cj0KCQjw4eaJBhDMARIsANhrQAB3PcQuPkDuszqzB44_daG7bfvQebpUVzpElH3qRsvcyXGUqnd05scaAvhOEALw_wcB
I hope this helps. If you have any further questions, please do not hesitate to ask.