Dual agetn authorisation

Has anyone worked with a situation where two professionals need agent authorisation for the same organisation at one time? We have been engaged to carry out a historical compliance check and disclosure to HMRC and then negotiate a settlement. In order to do that I need direct access to the compliance team and that requires agent authority. Problem is the payroll provider, who does not have the skills nor the insurance to do it, already has agent authorisation. Client wants to avoid any conflicts and ordinary payroll running problems and you can't get hold of HMRC! Done this kind of work before, lots of times but never met this situation.