Other FMS deals could be in the pipeline. Earlier this year, Defense News reported the British were in discussion with the United States over the possible purchase of Oshkosh-built Joint Light Tactical Vehicles.
The SSRO declined to comment on their move to bring G2G deals into the regulations.
But in the summary of a document published in September, titled "Perspectives on non-competitive defense spending," the organization argued that FMS generates transparency and justification issues that need scrutiny.
"Foreign military sales (for example, Poseidon P-8A and Apache helicopters) are decisions to award single source contracts which do not fall under the regulations and therefore do not benefit from the transparency brought by the regime. It is vital that there is transparency in all these cases and the reasons are fully justified," according to the SSRO.
Failure to open up G2G contracts can be counterproductive, according to Jon Louth, the director of defense, industry and society at the Royal United Services Institute think tank in London.
"The lack of transparency drives uncertainty and cynicism. Some of these deals are really good for the operator and can be good for the taxpayer as well. Having a light shine on these kind of contracts would not necessarily be a bad thing," Louth said.
Elements of an FMS contract may not get a nod of approval were they subject to the rules and regulations applied to a straight commercial deal with a company, Louth reckons. But, he said, there is another reason these deals need an independent review.
"Why are we having these deals unless we can point to them being specific and exceptional? Something like P-8 is a good example. It's difficult to see why it trumps other potential solutions other than the operators really wanted it, there's nothing wrong in that, but let's at least put it to some kind of scrutiny if we are going to have uncontested solutions" the analyst said.
In theory, at least the SSRO is meant to be independent of government, but questions are still raised over its relationship with the MoD. Louth said the legislation review will help bring the issue into view.
"There is a significant debate going on in and around Whitehall and Parliament as to the role of the organization. SSRO itself is very bullish and articulating the view that it wants to be an independent regulator and thinks there is an important role for it to play in that regard," he said.
"Other people have been pointing to a position within MoD which appears to drive it away from that independence. The fact that it has to take almost everything back to the defense secretary for approval makes for a really interesting agenda being played through the review at the moment. G2G and FMS is part of that debate," he added.
In an article on the "Perspectives on non-competitive defense spending" document, Louth questioned whether an independent regulator and adjudicator should be "subject to Ministerial whimsy."
"Credibility is key as the SSRO develops and the debate on where it sits within government should continue," he said.
Though not everyone agrees independence is an issue.
An article in the March edition of an in-house publication of ADS, the main aerospace and defense lobby group here, said industry reservations about the independence of the SSRO had "not materialized."
Earlier, the SSRO criticized industry and the MoD for failing to meet the new regulations and said it had identified up to £61 million in non-allowable costs claimed by contractors working under single-source contracts. These included costs for charitable donations, Christmas parties and staff welfare.