This is a requirements contract for the breakdown, repair and overhaul of equipment. Is the contractor subject to SCLS?
DAU's initial observation, based on the fact pattern provided in the Question Background, is that U.S. Government laws and regulations (including the FAR) should be applied to the U.S. subcontractor performing breakdown, repair, and overhaul of equipment tasks in the U.S. under the contract awarded to the foreign contractor (apparently located in the United Kingdom).
Whether or not the U.S. subcontractor should be exempt from U.S. law and FAR requirements with respect to Service Contract Labor Standards (SCLS) is less clear, however. The Question Background indicates that the work being peformed by the U.S. subcontractor could be eligible for an exemption from SCLS requirements if the UK prime contractor was willing to certify the validity of either the FAR 52.222-48 or FAR 52.222-52 exemption from SCLS requirements. It would seem that such a certifcation under either FAR part, if supported by the facts involved in this situation, would be in the UK prime contractor's interest.
In view of the ambiguities involved in the fact pattern, DAU recommends the questioner seek advice through the Department of the Air Force contracting 'chain of command' in the event that the UK prime contractor remains unwilling to certify that it is eligble for either a FAR 52.222-48 or FAR 52.222-52 exemption from SCLS requirements with respect to work performed by the U.S. subcontractor in the U.S. under this contract with the UK prime contractor.
The Office of SecDef (Acquisition & Sustainment), Director Pricing and Contracting, International Contracting organization may also be able to assist since they are the point of contact for Reciprocal Defense Procurement (RDP) international contracting issues that arise with UK contractors per the U.S DoD.-UK MOD RDP MOU. See URL https://www.acq.osd.mil/dpap/cpic/ic/reciprocal_procurement_memoranda_of_understanding.html to obtain a copy of this RDP MOU and/or further assistance from A&S/DPC/CPIC.