Ofcom is the UK gov department in charge of radiowave licencing. Equivalent of US FCC
As a ham I have a licence with them. But so dose all your WiFi equipment and phones have to meet there rules. Licencing can apply to a person, org or a device design depending on the frequencies used.
Every nation that is a member of the ITU. International telecommunications union.(Almost all nations) Has to have an agency enforcing agreed to rules.
So credibility on that subject yes. Very much.
But on mental effect on groups of people. They have 0 expertise. And given the numbers used (38men able to self exclude based on subject of study). None on statistical analysis.
Id only trust them on radio wave propergation, electromagnetic effect and licencing laws.
Here my own experience talking to folks working there. Get past the telephone handlers and they are real experts.