Conservative ministers have been accused by Labour of trying to push through billions of pounds in controversial pet projects before May’s general election, including the construction of a youth super-prison and further privatisation deals.

Sadiq Khan, the shadow justice secretary, said he was worried his prospective department would face a multimillion-pound bill to undo deals for the construction of a giant £83m Leicestershire prison for young offenders, which is strongly opposed by children’s charities. The government is trying to push legislation through the House of Commons to enable the jail’s construction.

“It’s wrong for ministers to put pen to paper and sign contracts for the construction of this jail,” Khan said. “In their headlong rush, they’ll commit a future change of government to their silly and ill-thought-through plans, lumbering the taxpayer with a huge bill for an unwanted kids’ prison ... If Labour wins, I’ll cancel the secure college plans and consign to the dustbin this terrible mistake”.

The shadow justice secretary has written to Ursula Brennan, the permanent secretary of the Ministry of Justice, arguing the deal should not proceed before May. An MoJ spokesman said the department would respond in due course once the letter had arrived.

“Secure colleges will be a pioneering approach to youth custody, with education at the centre,” the government spokesman said. “By moving away from the traditional environment of bars on windows and giving these young people skills, qualifications and self-discipline, we will be helping them turn their back on crime and become productive members of society.”

There has already been a rush of big contracts signed in recent months, including several for the £450m privatisation of the probation service, the £140m privatisation of the defence maintenance division of the Ministry of Defence and the £1bn privatisation of the east coast mainline rail service, which is going ahead on 1 March despite Labour’s opposition.

Chris Bryant, the shadow arts minister, raised concerns about the government trying to push through a complicated £5bn deal to eradicate mobile phone black spots. He told the Guardian he is “not yet convinced it is a good deal for the taxpayer” and Labour believes the deal has not been subject to proper scrutiny.

In home affairs, Jack Dromey, the shadow policing minister, has complained of the “unseemly haste” with which Theresa May’s Home Office is trying to push through a deal – worth between £500m and £1bn – to get private mobile phone companies to manage the communications network of the emergency services.

Vernon Coaker, the shadow defence secretary, raised the alarm about billions of pounds of defence contracts that are due to be signed early this year.

“Following the government’s botched procurement reform, which wasted millions of pounds of taxpayers’ money, the public will want reassurance that ministers are not rushing through important defence contracts at the last minute, ahead of the general election,” he said.

“It is essential that future contracts offer the best value for money, have robust bidding processes in place, and that they provide quality equipment or services for the UK’s armed forces.”