after doing the catch can mod,my plug has come out of the intake plenum,as a result the cel has come on,i drove home (about 6 miles),then re plugged the plenm,my question is do i need vagcom on it to re set the cel,or could me having unmetered air rushing in have caused somthing more sinister?

Basically you were sucking in unfiltered air.

Not sure what would cause the CEL to come on, I'm no mechanic, but I have a feeling you will need to have it reset with vag com.

Best plug for the intake is a 25mm plastic cap from BNQ

It has small clips on it so it shouldnt come loose