According to Livingstone, his motive is to improve the lot of London commuters by generating new funds to improve the Tube network. Yet his antipathy to Associated is well known and his long-running war of words with another Associated paper - the Evening Standard - has culminated in a month's suspension from his Mayoral office.
He has previously accused Metro of underpaying for the morning Tube contract, suggesting it amounted to only £1m a year - in fact the sum is £4.6m, comprising £2.6m in cash and £2m in free advertising. So it is a safe bet that the prospect of Associated winning the afternoon contract, which might see the hated Standard put out its Lite edition on his beloved Tube network, is one that fills him with horror.
If, as Livingstone has previously stated, the contract goes to the highest bidder, this prospect is a highly likely outcome. Associated, which can use its Evening Standard vans and drivers to transport papers around the city, has huge cost advantages over rival bidders for the contract. And its aggression in protecting its lucrative London franchise is legendary.
Of course, Livingstone could always renege on his original promise. The production of a contract tender document, due out in the summer, is eagerly anticipated. Will it, as is being rumoured, include qualitative elements - bidders' propriety as publishers and the "quality" of their product - that would allow Livingstone enough scope to scupper Associated's bid?
Yet such a move, aside from the prospect of legal challenges, could lead to a bid being accepted that wasn't the highest. In any case, potential bidders say that Livingstone is highly unlikely to get the £10m he has said he expects to get from the two contracts - which values the afternoon contract at £5m.
Metro targets commuters on their journey into work through about 400 Tube and train stations, but the number of stations entered by commuters returning home could be as few as 50.
This means fewer papers can be distributed at the start of an afternoon journey and some potential bidders put the value of an afternoon contract at less than £1m.
Such a paltry return for the Tube would leave Livingstone exposed to accusations that he is motivated more by politics than business.
- Colin Grimshaw is the deputy editor of Media Week.