Sir Richard Branson and the boss of FirstGroup, Tim O'Toole, will be questioned by MPs later over the controversial awarding of the West Coast rail contract
Virgin has been campaigning for a judicial review after the Department of Transport stripped it of the franchise - which stretches from London to Glasgow - and awarded it to FirstGroup.
Sir Richard is expected to use his time in front of the Transport Select Committee to argue that the rival company cannot afford the £5.5bn contract and that Virgin would deliver a better deal for passengers.
But Mr O'Toole will defend his company's bid, arguing that the process through which it was awarded the contract was "rigorous, detailed and fair".
The Government has already delayed the signing of the contract and, if approved, a judicial review could push back the handover from its scheduled date of December 9.
In the meantime, Virgin, which has run the line since 1997, has offered to continue operating it free of charge to allow the decision to be reexamined.
The Department for Transport is also thought be considering nationalising the line temporarily, according to media reports.
The latest development in the ongoing contract dispute comes after more than 170,000 people - including Mo Farah, Lord Sugar and Jamie Oliver - signed an e-petition calling for a rethink.
The rival bosses are due to appear before the Transport Select Committee soon after 4pm.
The committee's chairman, Louise Ellman, had previously urged Transport Secretary Justine Greening to allow the group of MPs to scrutinise the deal before it was signed off.
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