Witnesses have said that after eating at Zizzi’s restaurant they went to the Mill pub where Mr Skripal appeared unsteady on his feet, as if “drunk” – even though he had only ordered a single glass of white wine – suggesting the effects of the nerve agent were rapidly taking effect.Scotland Yard said there were no plans at this stage to release images from the CCTV footage.A spokesman said: “As with any inquiry CCTV forms a major part of it and a wideranging investigation into a number of areas is currently underway.”At a cost of £400,000 Salisbury’s CCTV is a state of the art colour system with high picture quality, even at night. It has suffered glitches and breakdowns in the past 12 months, following its introduction, but was by chance full operational in the weeks leading up to the nerve agent attack. “The coverage is extensive and very good, including around the Maltings shopping centre area where the Skripals were found,” said Salisbury council leader Matthew Dean. “If there’s something there to be seen the police will see it.” Sources have told the Telegraph that detectives are particularly keen to see if anyone followed Mr Skripal and his daughter from his home to a cemetery, or the town centre Zizzi’s restaurant and a local pub.They were found slumped on a bench on the banks of the River Avon at around 4.15pm on March 3. Eyewitnesses said they appeared “catatonic”.The father and daughter remained in a critical condition, while Det Sgt Bailey, 38, was seriously ill but stable. A further 18 people were treated for “minor side effects”. Officers from Scotland Yard’s Counter Terrorism Command are poring over hours of footage searching for vital clues to identify who attacked the father and daughter with a nerve agent. CCTV dated approximately one week before the murder of Sergei Skripal.Credit: ITV NEWS Sergei Skripal and daughter Yulia are critically ill. The police sergeant who was left seriously injured by a nerve agent while investigating the poisoning of a former Russian agent says he is not a hero. Credit:PA Police have identified more than 240 witnesses and are analysing more than 200 pieces of evidence in what Home Secretary Amber Rudd described as an investigation proceeding with “speed and professionalism”.John Glen, the economic secretary to the Treasury and Conservative MP for Salisbury, said: “A large amount of CCTV footage has been handed over and has been materially useful to the investigation. This material comes from functioning cameras of high quality with good coverage of the relevant areas.”Mr Glen added: “The hope would undoubtedly be that you might see something on there that would provide a clue to what happened, such as them being followed by someone.”The meticulous examination of anything that may have been contaminated by the nerve agent continued on Saturday as an ambulance was removed from an ambulance station on the edge of the city. The police officer who is seriously ill after helping a Russian spy and his daughter poisoned in a nerve agent attack has insisted he is not a hero but was “merely doing his job”.Detective Sergeant Nick Bailey is in intensive care after becoming contaminated as he went to the aid of Sergei Skripal, 66, and his daughter Yulia, 33, in Salisbury last Sunday.A statement issued last night through Wiltshire Police on his behalf said: “He wants to say that he does not consider himself a ‘hero’, he states he was merely doing his job – a job he loves and is immensely proud of – just like all of his other dedicated colleagues do, day in-day out, in order to protect the public and keep people safe.”He also thanked the public for their messages of support for him. The announcement from the officer, who can sit and up and speak, came as it emerged that the investigation was on the verge of a significant breakthrough after “materially useful” CCTV footage was uncovered. More than 200 pieces of evidence have been found. It has not yet been established whether the nerve agent was administered inside Mr Skripal’s home, through a contaminated gift unwittingly brought by Yulia from Moscow, or somewhere in Salisbury town centre. Another theory is that they were targeted at the cemetery as they lay flowers.Det Sgt Bailey was one of the first emergency personnel to visit Mr Skripal’s home after attending to the pair on the bench near the Maltings shopping precinct after a member of the public raised the alarm, though this remains unconfirmed by Scotland Yard. It remains unclear whether he was ingested some of the nerve agent at home or while with the Skirpals. His police car has also been seized for examination.A close relative of DS Bailey said it was her understanding that he had been among the first to attend to the Skripals in Salisbury town centre, before going on to the Russian spy’s £260,000 semi-detached house.She said: “He was at both places. First he was where they collapsed, trying to help them, then he went to the house, in that order.” Sergei Skripal and daughter Yulia are critically ill. Credit:Eddie Mulholland Soldiers wearing chemical protection suits, plastic gloves and gas masks covered the vehicle in protective sheeting before it was loaded onto a military low loader. It is thought the ambulance was used to ferry to hospital those people who helped the two Russians.The city’s cemetery where the spy’s wife, Liudmila Skripal, and son, Alexander, are buried remained sealed off yesterday as items placed by the father and daughter on the grave were analysed.A toy dog placed on Alexander’s grave, along with plastic flowers and a pot of real daffodils from both plots had been placed in hermetically sealed plastic bins and taken for analysis.The various routes the Skripals might have taken through the Cathedral city’s streets and pedestrian walks are overlooked by an extensive network of council operated security cameras, as is the main road the Skripals would have taken into town. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.