Having spent much of my working life working for computer and...

Having spent much of my working life working for computer and software companies in the public sector, governments use the expression of interest (EOI) approach the find out what options are out there with indicative costing..... a sneaky way of getting "free" consulting out of and prospective respondents.

They will then consolidate the 'Expressions of Interest' responses into either a request for proposal (RFP) or more likely a request for tender (RFT).

An RFT tends to be very prescriptive with little opportunity to be creative whereas an RFP is a much preferred option as it provides more flexibility in a response.

IMHO, CCE in responding to the EOI, will have a lot of scope and opportunities to propose a number of alternatives.... this is what governments are looking for when they release an EOI. If they really knew what they wanted, they would have released a very tightly prescripted tender