Dishwasher powdered detergent (W2 - Notting Hill Gate)

I would just need a little bit of powdered form detergent used in dishwashing machines - I don't have a dishwasher myself so buying a whole tub would not be practical. I have some fine metal mesh sprouter lids that need a heavy duty washing detergent at times. 200ml powdered detergent would go a long way, but even less will do :) If you are located near W2 that would be ideal. Thank you very much in case you read this and are able to offer some for me!