Can a controller be tasked to provide more than one ATC service at a time? During a visit to one of the ATC Facility  I found out that the Aerodrome Controller was also providing procedural approach control service along with aerodrome control service.

Similarly, Area Radar Controller of the same facility was also permitted to assume the responsibility of Procedural (Non Radar) controller (who acts as a backup to the Radar Controller) in the absence of Non Radar controller to provide relief to him.

I find both of these arrangements a violation of safety. I tried to find some reference to support my idea about this in the ICAO DOC 9426 (ATS Planing Manual) and Human factors Training in ATM, but could not find out anything that specifically prevents or allows this particular arrangement.

Can these services be combined? Any reference to the ICAO doc or some regulation would be a great help.
Since you've asked for a document, check ICAO Doc 4444:


  3.1.3.1 Where traffic demand varies significantly on a daily or periodic basis, facilities and procedures should be implemented to vary the number of operational sectors or working positions to meet the prevailing and anticipated demand. Applicable procedures should be contained in local instructions.


The ATS authority can indeed vary the number of working positions based on demand. The local instructions of the airport you visited will contain the details you need.