A strong second half for the home side. Three penalties plus a try from Hudson Tonga'uiha killed the game off.
The Pirates didn't give up and pulled a late try back from Ryan Storer, but this was cancelled out by Jack Moates.
So defeat on the night and on aggregate secures London Welsh the Championship trophy.
Welsh are now expected to take legal action over the RFU's ruling that they are not eligible for promotion to the Premiership.
More top news
Hundreds turned out to pay tribute to "Dancing Ken" whose funeral was held in Cheltenham this afternoon.
Feeling cold and still cloudy in the West but fewer showers than earlier in the week.
It'll be a cloudy day for most of Thursday with fewer showers than earlier in the week but still feeling cool.