Top executives of some large U.K.-based design and program management firms have joined professional service companies in non-construction sectors in a July 2 open letter to Prime Minister Theresa May that seeks clearer guidance on Brexit-related business issues.

The total of 42 signatories to the letter from the Professional Services Business Council includes leaders of AECOM, Arup, Make Architects, the Royal Institute of British Architects and JLL.

Terming professional services “one of Britain’s greatest hidden exports” that employs 4.6 million people, the execs want May’s Brexit talks with the European Union on trade and manufacturing also to “take our needs into account.”

Services are “inextricably linked, not separate,” the letter said. “The U.K. needs to get the right deal on professional and other services given our relative strengths and current competitive position.”

The council seeks to insure that professional qualifications and licenses, data protection and data-sharing rules, and legal judgments, among other business issues in the U.K. and in the 27-nation EU, still are “mutually recognized.”

Separately, Britain’s Construction Industry Training Board found that less than one-third of about 400 industry employers surveyed have implemented post-Brexit approaches to training and recruitment or plan to.