The House of Lords may have a valid point here but I can remember when smoking was allowed on all flights. The cabin would rapidly fill with the smoke from burning cigarettes to the point that even the smokers amongst the cabin crew would complain.
According to their Nobel Lordships, this was impossible as the entire air was changed every three minutes.
And yet, when the flight deck turned off the re-circ fans the cabin smoke would clear in about two minutes.
QED, re-circ fans do what is says on the can-and it doesn't say that it changes the air every three minutes. It says that they significantly reduce the need for bleed air off the compressors thereby decreasing fuel burn.
As to the filters, can we hear the views of the ground engineers who actually see them and hopefully get to change them? As far as I can remember, they filter out very little.