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
A bright start on Friday, although one or two showers will continue in the west.
It will become sunny for most people on Friday.
The Totnes MP says she's proud to have voted for a change to the EU withdrawal bill that allows MPs to have a meaningful vote on the deal.