A three-try blast in the first 30 minutes was enough to give Stevenage Town a 36-7 win over Welwyn at Allianz Park and take the Herts Presidents’ Tankard.
Datchworth completed the London Three North West double over local rivals Hitchin to secure a top half finish on the final day of the season.
Welwyn RFC suffered relegation from London Two North West on Saturday.
Welwyn RFC left Hurlingham Park on Saturday knowing their chances of avoiding relegation from London League Two North West now rest in the hands of others.
Datchworth lost 35-17 at St Albans which means they are not entirely safe from relegation going into the final league match of the season.