Labour is coming under increasing pressure after it refused to condemn the wave of strikes on one of Britain’s biggest rail networks in the run up to Christmas.

Staff on the Aslef and RMT unions began a 48-hour walkout at 12am and a further one-day strike is scheduled for Friday on the Southern Rail route in a dispute over the expansion of driver-only operated trains.

The entirety of Southern’s 2,242 daily weekday services have been cancelled after its parent company, Govia Thameslink Railway, failed in a last-ditch bid to halt the industrial action.

Chris Grayling, the transport secretary who is frequently used as a Tory attack dog, claimed that rail unions had threatened a decade of strikes. In a letter to MPs he also alleged Aslef and RMT had failed to accept an offer for talks with conciliation service Acas – although he did not provide any evidence and the unions said a proper negotiation had not been on offer.

Labour yesterday released a carefully-worded statement in which warned of the safety of Southern’s services but did not condemn the strikes.

“To attempt to pin the blame for Southern’s miserable service on trade unions rather than the incompetence of management and government ministers is an insult to long suffering passengers,” said Andy McDonald, the shadow transport secretary.

“As commuters are well aware, Southern’s sub-standard service predates any industrial action and trains are cancelled, late and dangerously overcrowded every day regardless of strike action.”

“Rather than playing the blame game, the Government should accept responsibility for the unacceptable service commuters are subject to and focus on resolving the dispute, as recommended by the Transport Select Committee.”

“The truth is that ministers are defending this failed franchise as a point of political pride when they should be sticking up for taxpayers and commuters.”

Southern has said the strike is “totally unjustified and totally unnecessary” and called on unions to work with it to modernise the railways.

The dispute has evoked memories of 2011, when Ed Miliband criticised a wave of strikes but in a television clip, but refused to say more when pressed by broadcasters.

Last month Grayling refused the request by Sadiq Khan, the London mayor, give him, through Transport for London, control of the failing franchise.

Last week it emerged that Grayling had sent a letter in 2011 where he stated his opposition to devolution on the suburban rail franchises for fear of them falling into “the clutches of a Labour mayor”.