The closure of the Forensic Science Service has been so rushed that police forces have been forced to turn to untested private suppliers to fill the gap, a police authority has warned.

Andrew White, the chief executive of the Hertfordshire police authority, said he had no choice but to sign off new contracts without doing the usual due diligence after being told that if they were not in place by the middle of July, there would be no access to forensic services in October. "This was not considered an option," he said.

Hertfordshire is one of 10 forces, including Hampshire, Kent and the City of London, in a joint competitive tendering exercise to replace the Forensic Science Service (FSS). The contracts range from simple DNA analysis from swabs taken when people are arrested, through to specialist support at crime scenes, including murder and rape.

Closure of the FSS was announced last December by the home secretary, Theresa May, because the government-owned company had been losing £2m a month and was at risk of going into administration. Its operations are to be sold or transferred before it closes next March.

The process has already been sharply criticised by MPs, with the Commons science and technology select committee calling last month for a six-month extension to the closure deadline because they were not confident an orderly transition could be achieved.

"Unfortunately, the process was extremely rushed and it was not possible to exercise the usual due diligence before signing these contracts," White said in a report to the last meeting of Hertfordshire police authority.

"The contracts seek to ensure quality standards, as did the procurement process, but it should be noted that many of these suppliers are relatively untested in this country and they are all having to build capability to cope with additional work from the UK police service.

"It has also not been possible to undertake any comprehensive benchmarking of pricing and some of the awarded prices do appear to be higher than that currently being paid to the FSS," he added.

White said that "in normal circumstances" he would have delayed signing the two-year contracts until further assurances on cost, quality and resilience had been obtained. But, he said, "given the clear statement that if we did not have signed contracts in place by the middle of July, we would not have forensic provision in October, this was not considered an option."

It is understood that Hertfordshire have received some assurances on price and quality since they signed the contract, but White also says only three days before the contracts were signed the Home Office approached the authority to wait until a private buyer could be found for parts of the FSS. White said this option was rejected as not being viable given the short timescales.

Companies awarded the main Hertfordshire contracts include Orchid Cellmark, LGC and Key Forensics.

The Home Office said that forces involved in the competitive tendering process, overseen by the National Police Improvement Agency and the Association of Chief Police Officers, were not rushed into a decision. "All police forces had the option to continue as customers of the FSS until a buyer is found, or to procure new contracts. As former customers of the FSS, Hertfordshire police made clear their decision was to seek new arrangements and we are working with them and several other forces to take this forward," a spokeswoman said.

"The national forensic framework agreement procurement process allows all police authorities to secure the best value for money in local forensics provision. This has delivered reduced prices and better turnaround times and will deliver significant savings at a national level."

A shadow Home Office minister, Shabana Mahmood, said police forces were being put in an impossible position: "This is extremely serious. For the home secretary to have put police forces in this position just goes to show the degree of incompetence from this Government on policing and crime policy.

"This example shows that because of Government cuts and poor Home Office planning, a high quality service that provided good value for money is in danger of becoming more expensive and with less quality-assurance," she said.

"This work is of vital importance, ranging from DNA analysis, taking swabs in custody and managing crime scenes. Yet the home secretary seems happy for contracts to be awarded to untested companies, lacking capacity, with a rushed procurement process."

"All this at a time when police forces across the country are struggling with cuts to 16,000 police officers, curbs in DNA use for serious offences, and a Home Secretary focused on rhetoric rather than the reality on the ground. She is putting Police Forces in an impossible position."