Like Mr Mac, not only do I rarely stick my head above the parapet on this forum, but i also come from a construction background.......
Back in the good old days, government building works including military facilities came under the auspices of the PSA, Property Services Agency. Whilst they were speaking as a contractor, without doubt a pain in the ar*e to work for, they did know what they were doing. They had their own architects and engineers both structural and MEP (mechanical, electrical & plumbing), everything was designed and built to a standard that had been formulated by many years of experience. Then they got sold to Carillion (remember them? Formally known as Tarmac) and under the guise of saving money, they had to bid for government work in competition with the private sector. This meant that building works got designed and built to a price, not a standard. It also meant that the knowledge built up over many years of how to do things was no longer available and all over the government estate, architects and engineers were reinventing the wheel and designing as cheap as there PI could stand.
Same happened in the NHS who also had their own architects and engineers who also knew what they were doing. And the Post Office who also did there own MEP installation works inhouse with their own directly directly employed workforce.
I believe McDonald's still has it's own inhouse design team.