The family of a woman killed in the Wiltshire novichok poisonings more than four years ago has expressed concern that there is still no start date for the full independent inquiry into her death despite it raising pressing national security issues. Lawyers for relatives of Dawn Sturgess said there had been “substantial” delays and called for the preparation process to be speeded up and for extra resources to be made available if necessary. The UK government said tens of thousands of documents had to be painstakingly sifted through to prevent secret information being released that could help an enemy state carry out more attacks. The former Russian spy Sergei Skripal was the target of a novichok poisoning in Salisbury in March 2018. He, his daughter Yulia, and the police officer DS Nick Bailey were poisoned but survived. Four months later, Sturgess, a 44-year-old mother of three, and her partner, Charlie Rowley, were also poisoned after he found a fake perfume bottle containing novichok. Rowley recovered but Sturgess died on 8 July. At a third preliminary inquiry hearing in London, Michael Mansfield KC, who represents the Sturgess family and Rowley, characterised the delays as “substantial”. He said the family understood the difficulties the government faced but called for pressure to be put on everybody involved to ensure the full inquiry took place as soon as possible. Mansfield said: “If there is a need for more resources, perhaps now is the time to indicate that considering that this inquiry is dealing with the matters of the utmost importance, dealing with national security.” He claimed there had already been a “12-month slippage” on the start date for the full hearing. “There was originally a hint that it might have started at the beginning of this year,” he said. The hearing was told the delays had been caused by the disclosure process under which evidence from the police and others was provided to the inquiry and then passed on to core participants such as the Sturgess family. Andrew O’Connor KC, the counsel for the inquiry, said the difficulty and length of disclosure was a “striking” feature and delays were “unfortunate”. O’Connor said that in the last few months this delay had been “unblocked” and the the team had now received more than 28,000 documents from counter-terrorism police via the government. But so far only 40 documents had been passed to core participants. The vast bulk of the material has been held back pending rulings over what elements of this material must be kept secret because it is so sensitive. O’Connor also revealed that the former home secretary Priti Patel imposed a restriction notice on a small set of documents. The barrister said this was usually a decision left up to the inquiry chair. Cathryn McGahey KC, counsel for the government, said it was “hugely important” that nothing emerged in public that could help a hostile state or terrorist. “There has been no delay in the sense of needlessly wasted time,” she said. Lord Hughes of Ombersley, who is chairing the inquiry, ruled that the full inquiry should take place in Salisbury and London, and said it was essential that a date should be set at soon as possible. The UK government has blamed the Russian state for the novichok attack. Hughes said the government had not produced the evidence for its assertions at the time and made it clear part of his role was to test them.