The Battersea Power Station Community Group (BPSCG), with the Twentieth Century Society, claims not enough has been done to protect Giles Gilbert Scott's stacks.
The BPSCG also questioned a report by engineer Buro Happold, whose advice was used to justify a planning application by developer Parkview International to demolish the chimneys.
English Heritage (EH) is only now studying the stacks since joining a steering group
in 2004 to assess and fix them.
EH London region director Philip Davies tried to reassure the BPSCG of the building's safety in a letter last year.
He wrote that EH was visiting the site regularly to 'ensure that there is not rapid deterioration that may put at risk the viability of the future restoration proposals'.
BPSCG member and conservation architect Keith Garner slammed this pledge. He told the AJ: 'Davies has failed in his aim. EH could have laid down the law a lot earlier. They've not been diligent in making Parkview look after
the building. If Parkview had started a phased series of repairs since taking charge of the building in 1993 there would have been a much better chance of saving the chimneys. The results of this report are questionable.'
The author of the report, structural engineer and Buro Happold associate Jim Solomon, denies anything more could have been done to save the stacks. He claims a high level of chloride in the concrete has been there from the beginning. This could be because the water used was Thames saltwater, he said.
Parkview International lodged a planning application with Wandsworth council on 11 July to redevelop the building, including permission to rebuild the chimneys. The developer's director of design development, Steve Kennard, has claimed commercial issues prevented a full survey until recently.
He said: 'We have always known that the building's fabric generally was in a poor state and that there were problems with the chimneys.
'We have reached the conclusion that we need to demolish the chimneys after a two-year examination of the whole building. Annex B was leased to the London Electricity Board until spring 2003. Once we had the whole building back we had the opportunity to survey it, including the chimneys. That process cost a great deal of money and was related to the commercial certainty of the project.'
EH issued a statement saying: 'We have been working with developer Parkview International and Wandsworth council over the last two years to develop proposals for the reuse of the power station.
We have also been closely involved in carrying out detailed investigations into its structural condition. The findings of these studies have been used to inform proposals for the repair and restoration of the building.'