The society submitted a renewed listing application for the building in August, after it emerged that Howells was planning to convert the landmark high rise into flats under permitted development rules.The heritage campaign group had previously said that while it supported plans for the buildings residential conversion in principle, 'a sympathetic approach to any works [was] essential'.Its listing bid followed an earlier unsuccessful attempt to protect the building 12 years ago.AdvertisementPosting on Bluesky, the society said it was disappointing news that its second attempt had failed, insisting that the building was Seiferts most significant tower to remain unlisted.The 24-storey office block at 12-16 Addiscombe Road, next to East Croydon station, opened in 1970 as the headquarters of Noble Lowndes Annuities (NLA). It is also known as No 1 Croydon as well as the 50p or Thrupenny Bit building.Under Howells proposals, no external alterations would be made to the tower, which would be converted into 250 self-contained flats. These would range in size from 38m to 73m, with the number of homes per floor varying between 10 and 12.In 2013, Historic England (then English Heritage) rejected a bid from the Twentieth Century Society to Grade II list the building on architecture and planning grounds.At the time, the government's heritage watchdog said the building had been very carefully considered against Seifert & Partners body of work, as well as in comparison with other contemporary office blocks and did not meet the necessarily strict criteria of special interest required for post-war buildings.AdvertisementA spokesperson added in 2013: The design lacks the sophistication of Seiferts best projects and the poor quality integrally designed landscaping detracts from the value of the whole scheme.Speaking about No 1 Croydon after the latest listing application was submitted, a Twentieth Century Society spokesperson told the AJ: The recent renovations and conversions of Seiferts other listed buildings Centre Point and Space House in London, and Alpha Tower in Birmingham (all at Grade II) have demonstrated the growing appreciation in the practices work and how the heritage status of these buildings has proven to be an asset in developing and marketing them.A prior approval notice for the buildings change of use was submitted to Croydon Council on behalf of Britel Fund Trustees in July 2024.Permitted development rules allowing homes to be built in former commercial premises have proved controversial in the past, prompting claims that the policy was creating slums of the future.In 2014, Croydon Council introduced a ban on permitted development schemes in the borough after a slew of office-to-resi conversions. That block has now expired.Howells has been contacted for comment.CommentColm Lacey, managing director of Soft Cities and former chief executive of Croydon Council's housing developer Brick By BrickAt first glance, the proposals for the NLA tower look like an interesting conversion of a much-loved local landmark, with the majority of the flats meeting minimum space standards and presenting a workable domestic layout. There remain some issues not least the apparent absence of affordable housing tenures and the perennial office-to-resi challenge of multiple single-aspect units.The scheme raises an interesting question as to whether decent quality permitted development (PD) conversions offer more security for the architectural integrity of office buildings in outer London than their more commercially perilous extant uses. In this case, it should be noted that the unfortunate ground-floor extension, which blights the otherwise original composition, is a wholly commercial retail addition.Croydon has suffered badly from extremely poor quality PD conversions in the past, and at present the quality (and tenure mix) of such developments remains driven by developer sentiment rather than regulatory policy. One would hope that the current planning reform process might begin to tackle the need for a simple, workable policy which enables the right kind of office-to-resi (and retail-to-resi) conversion.