doubling the number ordered reduces the price across the board.
isn't that a false argument?
The MOD buys 100 at £100 a pop. Later a foreign AF buys 100 and pays £50 a pop. The average cost is now £75. Does the MOD get a refund? No because that £25 is notional, no money changed hands.
OTOH, if 4 Governments at the outset bought 400 the cost would only be - wait for it - £100 a pop.
The only winners after the initial order are the companies and the MOD on follow on orders. Then the MOD can apply cost averaging.