MI6 is really going into the realm of creative imagination whether trained by them or its them. Imagine how silly its sounds to spend all that money on such training to infiltrate singapore opposition parties. All these infiltration can be done by junior handlers in any intelligence outfit. Political parties are super poor and are struggling to make ends meet, and trying to best to hold to the few good people they have. They don't have the means and time to run sophisticated clandestine operations requiring covert skills from MI6. .
MI6 trained doesn't mean he was sent for training specifically to infiltrate opposition. He could have had another assignment before like ISD terrorist unit.
i suspect only those "cannot make it" operatives are sent to oppo parties. the good ones either spy on PAP grassroots to make sure the slate it kept clean or army units which is a prime target for "disruption" by undesirable elements.