100% agree with Germanshepherdsmum. SARS Covid is a multi-system disease and the consequences, which may not be felt until weeks or many months post infection, can be life-long, devastating or fatal. There have been plenty of peer-reviewed research papers written in the last 4 years to evidence this.
What a horrible person your son's boss is! Why on earth would he think it appropriate to make anyone so obviously ill (whatever the cause) to travel to a social event? Does he get some kind of financial penalty or something if all employees don't attend?
Your son did absolutely the right thing. Who knows who he may have infected either on the journey or while at the event - possibly someone who lives with a vulnerable person.
Unfortunately, the UK government has decided that the health & well-being of the people are less important than capitalism. Legislation could easily have been passed to ensure safe, clean air in workplaces, schools and public places, just like they had installed in the Houses of Parliament. Call me cynical but I don't think it was a coincidence that the December Covid statistics were not released……wouldn't do to take the shine off the festive shopping and frivolities would it?