This final phase of engine development should get under way in earnest at the start of next year, and, once again, it will be supported by Esa.
The agency's propulsion experts will offer their insights on many technical aspects of the programme, but they plan also to provide due diligence to ensure REL delivers against milestones.
The desire is to have a full set of engineering drawings completed by the end of 2017 that would enable a real flight model of Sabre to be manufactured.
Before then, REL hopes also to have produced a ground demonstrator.
"I always liken the demonstrator to a dissected rabbit, with all its organs spread out," explained Mr Bond.
"It would not resemble a flight engine, but it will have all the correct features of a real engine, and it will show that it's controllable, that it's self-sustaining and indeed that it can simulate operation from take-off conditions."
The head of Esa's mechanical engineering department, Constantinos Stavrinidis, said the agency took the view that Sabre was a realisable technology, but that it might be some years yet before the engine got into the skies.
"It took a while before steamships took over from clippers; it took a while before jet engines took over from propellers. But I'm convinced this is the last frontier: utilising oxygen from the atmosphere. This technology - the heat exchanger - has demonstrated that it can work," he told BBC News.
Sabre engine: How the recent "proof of principle" experiments were conducted