The Department for Transport is planning to appoint a "shadow operator" to help it introduce additional Pendolino carriages on the West Coast Main Line.

A shortlist of up to five bidders will be announced in May with the contract awarded in August.

The new tactic from the DfT follows the failure of negotiations with Virgin to lengthen the entire fleet from nine to 11 cars and introduce an additional four 11-car units progressively before 2011. The DfT expects that the project will be delivered more cheaply through competitive tender than single party negotiation.

However, it could result in no additional Pendolinos entering service before the next franchise starts in four years. The programme could also be reduced in scope with the DfT reserving the option to lengthen just 31 of the existing 52 train sets to 11 cars. It will decide by September 2010.

The DfT's brief to the shadow operator will be to assist with the procurement, design and delivery of new vehicles, test them and ensure depot facilities and platforms can accommodate the enlarged fleet.

It will be required to clear four new nine-car sets for service, then lengthen them to 11 car and take the longer sets through testing so that they are available for when the new West Coast contract begins in April 2012 (if agreement can be reached with Virgin, the DfT said these trains could enter service earlier).

The new franchise operator will lengthen the rest of the fleet with the target of completion by the end of 2012. As well as having the option to lengthen just 31 of the existing sets, depending on passenger growth, the DfT has signalled that a 'later option' could be to order an additional 23 Pendolino sets to displace the West Coast Voyager fleet and provide further new capacity.