The Government has invited agencies to apply as part of a formal tendering process, which began this week after what it called "an extensive period of consultation" with the ad industry.
The potential involvement of Truth, which styles itself as a blockchain media agency, is a shock move that suggests the Government is willing to consider radical options – at least at the start of the formal process.
The other contenders are believed to be the big four media-buying groups: the incumbent, Dentsu Aegis Network, and WPP, Publicis Groupe and Omnicom.
Industry sources say the Government held a conference call with the five agencies last week.
A Cabinet Office spokesman said the tendering process is open and any agency can still apply at this stage.
The spokesman added it could not comment on the identity of any agency or confirm how many are involved in the process.
None of the agencies would comment.
The Marketing Group, a mini-holding company based in the UK and listed on the Nasdaq Stockholm stock exchange since 2016, only launched Truth last November.
Truth has claimed that its use of blockchain technology, which acts as an online ledger to record transactions digitally, means it is transparent and accountable.
The Government first announced plans for the statutory review in October 2017 with a pledge that transparency would be at its heart.
Alex Aiken, the executive director of Government Communications, wrote in an article for Campaign that it would run an "open and transparent" process and it expected agencies to offer the same commitment in return.
The Government is keen to avoid a repeat of the last review in 2014 when it awarded the account to Dentsu Aegis Network's Carat in what was widely seen as a price-driven process. WPP, the previous incumbent, went to the High Court to challenge the decision.
The Government Communications Service has said it wants the 2018 review to set "a positive example" to the ad industry.
Each bidder must "show it has experience in buying media on a similar scale and complexity" for "multiple clients" to be eligible to take part in the process.
Documents published by GCS on its website have stressed the importance of issues such as online brand safety, data protection and value for money for taxpayers.
The Government signalled that an agency's capabilities, quality of service and talent are more important criteria than pricing, which only counts for 10% of the final decision, according to one GCS document.
The Government is using PwC as an adviser on the pitch and has said it will use the principles from ISBA’s tougher, 2016 media agency framework contract in the review.
It is thought that a number of leading independent agencies may have considered pitching for the Government’s account but decided against it because of the scale of the account – one of the biggest in UK media.
Editor's note: The original version of this article quoted a GCS document that said any agency that puts in an offer to do the work for less than 95% of the value of Carat’s current contract would be considered to have made an "abnormally" low bid. However, the Cabinet Office contacted Campaign after publication to say the 95% figure was only included in a draft document and it has given new guidelines on media pricing and remuneration to agencies.