Wessely was unfortunately not mentioned. However a report at the time - the Clayton report, referred to in Hansard below clearly aims to minimise the effect of early issues and raises anxiety as an explanation in below (my bolding)
Hansard
https://api.parliament.uk/historic-hansard/written-answers/1989/jul/20/lowermoor-incident-group
"
Mr. Freeman
The report of the Lowermoor incident health advisory group is being published today. The group was set up in January 1989 at my request to provide independent expert advice to the Cornwall and Isles of Scilly district health authority on the implications for the health of the population in the Camelford area following the contamination of their drinking water in July 1988. Copies of the report have been sent to the Department of Health and to the Department of the Environment, and I am placing copies in the Library. I am grateful to Dame Barbara Clayton and her colleagues for their very thoughtful and authoritative report.
Hansard:
https://api.parliament.uk/historic-hansard/written-answers/1989/jul/20/lowermoor-incident-group
"The Government welcome the group's advice that no long-term effects on health are expected. The group's main findings are that:
(i) early symptoms, which were mostly gastrointestinal disturbances, rashes and mouth ulcers and which appeared to be mostly mild and short-lived, can most probably be attributed to the incident. Other causes such as viral infections cannot be discounted for some of the cases.
(ii)
it is not possible to attribute the very real current health complaints to the toxic effects of the incident, except insofar as they are the consequence of the sustained anxiety naturally felt by many people. A number of factors have contributed to this anxiety, particularly in relation to long-term effects, and these are addressed in the report."
Hansard
https://api.parliament.uk/historic-hansard/written-answers/1989/jul/20/lowermoor-incident-group"
I cannot find the full report, nor who the other authors were. In the film there is a brief shot of 4 people, including Clayton -but I don't know who the others were.
However I know how brilliant the S4ME sleuths are at finding relevant info.
