In my opinion, there are two parts to this. Once the Council has accepted a tender, the details of the contract become public under the Transparency Code and should be published annually. With this in mind, it should be possible for a resident to ask to see the information at any time. I would never withhold information that a resident could obtain through an FOI request.
The unsuccessful tenders may not be available, even through an FOI request. Paragraph 43(2) of the Freedom of Information Act states:-
43 Commercial interests.
(2) Information is exempt information if its disclosure under this Act would, or would be likely to, prejudice the commercial interests of any person (including the public authority holding it).
There are various tests that should be applied to determine the level of harm that might result from disclosure against the level of public benefit, but it is likely that such information would be exempt in most cases.