Ministers must answer questions over the “quick succession” of lone actor attacks in Britain, the shadow home secretary has said. Responding to a statement from Priti Patel, the home secretary, Nick Thomas-Symonds said it was “heartbreaking” that terrorism was once again being discussed in the House of Commons. His remarks came after Patel revealed that an unarmed police officer had tackled a suspected terrorist in the midst of a knife attack in Forbury Gardens in Reading on Saturday. The 25-year-old suspect was apprehended at “great speed”, Patel said, as she paid tribute to the bravery of the officers and members of public who intervened. If confirmed as a terrorist offence, the attack would be the fourth in the UK since November, when Usman Khan killed two people at Fishmongers’ Hall near London Bridge. There have since been terrorist attacks in Whitemoor prison in January and on Streatham High Street, in the capital, in February. The terrorism threat level remains “substantial”. “It is heartbreaking that we are having this conversation again so soon after the terrible attacks at Fishmongers’ Hall in November that tragically took the lives of Jack Merritt and Saskia Jones and the attack in Streatham in February,” said Thomas-Symonds. “This is a live investigation, so we have to ensure there is due process and that the police can do their job, but the country will want answers about these incidents which have occurred in such quick succession. “So whilst the priority today must be to ensure that there are no further related threats and that the victims and families are cared for, it is vital that questions are addressed.” Witnesses described horrific scenes in Forbury Gardens, a popular spot for families, as a man attacked several groups of people with a knife, killing three. Thames Valley police said they arrested a suspect within five minutes of the first call at 6.56pm on Saturday. In her statement to MPs, the home secretary described how “the armed suspect was tackled to the ground by an unarmed officer and was immediately arrested at the scene … Police have confirmed that the threat is contained, but that sadly three innocent members of the public were killed, murdered by a sudden and savage knife attacker as they enjoyed a summer evening with friends.” The home secretary said she had met the officers who responded to the incident, some of whom were student officers. “A young unarmed police officer took down the suspect without hesitation while another performed emergency first aid to those who were injured,” she said. “These officers are heroes. They show courage, bravery and selflessness way beyond their years. They are the very best of us.” Patel re-emphasised comments made by the prime minister, Boris Johnson, on Sunday that the government was ready to act on any lessons that emerge. She said: “We continue to pursue every option available to tackle the terrorist threat and to take dangerous people off our streets. “As the prime minister reiterated yesterday, the police and security services will continue in their investigations to better understand the circumstances of this tragic incident and if further action is needed, we will not hesitate. “Our world-class CT, police and security services have my unequivocal backing as they hunt down hate-fuelled terrorists and extremists. So my message today is clear, simple and strong: swift justice will be done, victims will be supported, and if further action is needed to stop terrorists in their tracks, this government will not hesitate to act.” Patel added that it was “clear that the threat posed by lone actors is growing”.