The Building Research Establishment published a series of reports in the 1980s to advise local councils and building owners on checking the structural stability of their LPS blocks. The contents of two of the reports relied on local authorities sending returns in to the Ministry of Housing and Local Government during 1968 and 1969. This was not exhaustive, with many authorities failing to do so and thus not having their blocks assessed after the issue of interim structural methods by the Ministry in 1968–69. Among these authorities were Lambeth and Southwark in London, and Birmingham. Birmingham owned over 300 LPS blocks, and when these were assessed in 1998 it was found that a number which did not meet 5 psi (34 kN/m2) still had a piped gas supply. A number of those blocks were demolished. The London Borough of Southwark owns the largest LPS estate in the UK, the Aylesbury Estate, which has a piped gas supply; it has been questioned whether the structure is strong enough to resist a 5 psi explosion. Southwark Council admitted 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.