Some confusion seems to have crept in. The council boss is described as the council's leader, i.e. its top politician/councillor, and not its chief executive, i.e. its top official/employee. Also, though chief executives and other very senior managers in councils have considerable authority and advise the senior councillors who make major decisions, the senior councillors tend to have ultimate authority and power. Therefore, the EHOs (environmental health officers) are far from being the council leader's co-workers as suggested by Stevie40. In addition to the difference in power and status, some council employees, including quite senior ones, nowadays are understandably fearful about their jobs/careers and may not wish to unduly rock the proverbial boat. This is a general comment and should not be construed as applying to the council involved in this case.
Other factors might include any previous less-than-positive attitude shown by the council leader to aspects of occupational safety & health (OS&H). As for how the principal contractor's people dealt with the situation at the time, they might have been influenced by fear, perceived or otherwise, that the firm might not win future contracts with the council. Anyhow, if there was a genuine need for helmets to be worn during the visit, all visitors, irrespective of status, etc., should have worn them.
It's also appropriate to add that some council leaders and chief executives do demonstrate a positive attitude to OS&H. For example, those of my employer routinely wear helmets when appropriate during visits to construction projects. They might even have their own helmets instead of having to borrow them. Also, both men liaise with my boss from time to time about critical OS&H matters - and, crucially, my boss can approach them when appropriate.
On a general note, judging from TV news and documentaries, various VIPs including members of the Royal Family, seem to have no problem with wearing helmets when appropriate. Even so, perhaps some people in the UK have a cultural/attitude issue about helmets and other types of personal protective equipment, i.e. such equipment is fine for workers, especially ones they perceive as being in menial positions, but is not appropriate for themselves. By contrast in the USA, for example, it seems that some or many people regard a helmet as a macho status symbol. Some US films and documentaries even portray people, usually blokes, wearing their helmets while shopping or driving. Can anyone with experience of the USA confirm or refute this impression?