The requirements to treat bidders equally and transparently is already there in the Public Contracts Regulations 2015 (PCR) and this continues via section 16 of the Act.
The difference under the Act is the new obligation at section 17 is to publish a Preliminary Market Engagement Notice (PME Notice) whenever the authority carries out preliminary market engagement (unless there are compelling reasons not to do so).
Whether this will lead to increased challenges (presumably on the basis that the preliminary market engagement has given a competitor an unfair advantage?) will presumably depend on the content requirements of the PME Notice.
The PME Notice will need to set out the requirements listed in regulation 17 of the Procurement Regulations 2024, which is essentially “a description of the process by which the contracting authority proposes to engage, or has engaged, with suppliers during the preliminary market engagement.”
The official guidance on preliminary market engagement suggests that “the notice can be used to share engagement outputs and ensure a wider audience is kept informed about the contracting authority's emerging thinking, therefore supporting the objectives of section 12 and ensuring all suppliers have access to the same information. The notice can also flag additional upcoming engagement opportunities.”
There does not appear to be anything in these requirements that means that the authority must for example, provide in the (public) PME Notice a list of every supplier it has engaged with, discussions had and outcomes arrived at (although of course it may be necessary to share this information with candidates/tenderers in a procurement in order to meet the duties at section 16 and the guidance certainly seems to point to it being best practice to give significant narrative detail in the PME Notice).
It certainly seems possible that increased transparency around PME Notices might lead to increased challenges – it will depend on the level of detail disclosed. It is of course always the case that, in order to bring a challenge, a supplier needs to show not only that there has been a breach, but that this has caused it to suffer or risk suffering a loss. Query if this might be difficult for a supplier to substantiate in relation to an alleged breach at PME stage.