to the cause". They specifically cover pressures which may be caused for example by wind forces, explosions (either internal or external), or vehicle incursions, and note that seismic design may occasionally be required. Immediately after the publication of the report the Government brought out interim measures to ensure the safety and integrity of buildings in the event of an explosion. All new buildings of over five storeys constructed after November 1968 were required to be able to resist an explosive force of . Existing buildings were allowed to resist an explosive force of , provided that the gas supply was removed and flats were refitted for electric cooking and heating. Many other jurisdictions, including the US, have since amended their building codes to require that buildings subject to explosions or other accidents will not collapse to an extent disproportionate to the cause. Two days after the Grenfell Tower fire in 2017, John Knapton, emeritus professor of structural engineering at Newcastle University, claimed that regulations which came into force in 1971, following lessons learned from Ronan Point, had improved building structural strength in such a way as to prevent the collapse of the Grenfell Tower, which was built in 1974. Effect on housing In 1985, the Building Research Establishment published a report entitled "The Structure of Ronan Point and other Taylor Woodrow – Anglian buildings" to advise local councils and building owners on checking the structural stability of their blocks. Southwark Council confirmed in 2017 that strengthening work ordered after Ronan Point may not have been carried out on the Ledbury Estate, after structural weaknesses were found that led to the evacuation of four tower blocks. Within a couple of decades of the collapse of Ronan Point, the public's lack of confidence in the construction technique used at Ronan Point, together with the social problems within such developments, led to the demolition of many tower blocks. In particular, the construction technique involved metal bolts which expand when they rust and crack the concrete round them. In 2018, it was reported that two tower blocks on the Broadwater Farm estate in Tottenham, Tangmere House and Northholt House, were structurally unsound and could collapse catastrophically if there is a gas explosion or if a vehicle collides with the base. Both are to be evacuated urgently. Other buildings in Broadwater Farm had less serious problems. Legacy In May 2018, 50 years after the partial