A policeman was sprayed in the face with a mystery substance outside Parliament by a suspect who fled the scene last night following a major security breach. The Metropolitan Police said the officer was attacked with the substance at around 8pm yesterday while on duty at the Palace of Westminster in Millbank, central London. Police are using a helicopter to search for the suspect, who ran in the direction of Victoria Tower Gardens after the incident. The officer suffered mild irritation to his face and was assessed by London Ambulance Service, Scotland Yard said. He did not require hospital treatment. It comes hours after a man was arrested after allegedly climbing over a fence at the Houses of Parliament before being pinned down by armed police. The suspect got through the gate in front of the building before officers dragged him to the ground. One photo shows the intruder clambering over two fences before being detained on the grass at New Palace Yard while police trained their guns on him. Another image showed a bike abandoned on the road just metres from Parliament. A later photo showed the man being guarded by two policemen with his arms bound behind his back in handcuffs. Scotland Yard said he was arrested at Carriage Gates on suspicion of trespassing on a protected site, but added it was not being treating as terror related. Last night the force said he remains in custody and enquiries are ongoing. The suspect made it through the same entrance where PC Keith Palmer was brutally murdered in a terrorist attack in 2017. It comes hours after a man was arrested after allegedly climbing over a fence at the Houses of Parliament before being Tasered and pinned down by armed police One photo showed the intruder - wearing a woolly hat, jeans and trainers - being arrested on the grass at New Palace Yard while police trained their guns on him Another pictured a bicycle abandoned on the road just metres away from Parliament, having covered most of the distance from the main road The suspect made it through the same entrance where PC Keith Palmer was brutally murdered in a terrorist attack in 2017 The man was hauled into the courtyard outside the building while shouting at the officers with their hands on his shoulders. He was later moved to another part of the grounds towards the exit while continuing to yell at the police. Officers then bundled him into the back of an arriving police van while he bawled: 'My rights.' Almost a dozen policemen formed a perimeter around the area while he was dealt with, having already been on the scene due to Prime Minister's Questions and a large protest in Parliament Square. The suspect made it through the same entrance where PC Keith Palmer (pictured) was brutally murdered in 2017 Elliot Keck, who works in the office of Romford MP Andrew Rosindell, said it appeared that the man had climbed over the fence before he was tasered by police. Mr Keck, 27, said: 'As he was being tasered two armed police had their guns drawn.' He added: 'When it was established he wasn't a threat armed police moved off and he was sat upright for a period before being taken to the van.' Mr Keck said the man had discarded a bag which was also searched by police. Another witness told the Mirror: 'Just saw someone climb into Parliament. Quickly tasered and guns immediately drawn. Impressive performance from the police.' The entrance has been the focus of previous attempts to get into Parliament, including the one that saw PC Palmer killed. Khalid Masood stabbed the officer to death in March 2017 as he forced his way through the gates. He was shot dead - but had already killed four others using a car on Westminster Bridge. MailOnline revealed in 2019 security spending had soared by nearly £10million a year since the deadly attack - up to an estimated £45million annually. The overhaul came amid fears about gaping loopholes, including weaknesses at Carriage Gates, no armed officers on site on Sundays, and poor CCTV coverage. Two separate reviews recommended sweeping changes to the defences on and around the estate. In April 2017 - three weeks after PC Palmer's death - larger and taller black iron security gates covered in wire mesh were up. They are now permanently closed unless a car requires access, but this was not the case when PC Palmer was murdered. Armed officers are also permanently on duty by the entrance. Details buried in the accounts for the Houses showed the total security bill for the Westminster estate came to £40.15million in the year following the terror attack. That was up from £35.24million in 2016-17. The entrance has been the focus of previous attempts to get into Parliament, including the one that saw PC Palmer killed (pictured) Khalid Masood (pictured above) stabbed the officer to death in March 2017 as he forced his way through the gates. He was shot dead - but had already killed four others using a car on Westminster Bridge A police officer lays a single rose by the memorial to honour PC Keith Palmer in March at 14.40, the time of the Westminster Bridge terror attack four years ago The Carriage Gates are pictured outside the Houses of Parliament which Masood was able to enter during his attack in 2017 The figure appears to have risen even further since then. The Houses split the costs on a 30-70 ratio, and Lords records show it has been contributing around £1.1million a month to security as of October. That would give a total annual bill across the estate of £45million. The bill does not include spending on cyber-security - which is also understood to have spiked amid fears over hacking attacks. A Met police spokesman said: 'At around 3pm on Wednesday, 1 December, a man was detained and arrested at Carriage Gates inside the Palace of Westminster on suspicion of trespassing on a protected site. 'Enquiries into the circumstances continue. This is not being treated as a terrorist incident.' Carriage Gates were briefly put on lockdown following the breach. A House of Commons spokesman said: 'We are aware of an incident on the Parliamentary estate which is being attended by police and security staff.' All rights reserved for this news site (dailymail) and under his responsibility