What is it?

We found this plant growing well in a now rather derelict part of the garden. The leaves look a bit like mint and the aroma is minty too. We wondered if it is mint. But the mint we have growing is in pots: it spreads too easily.
Plant net, an app for my phone solved the problem. It took this photo and compared the flower with the many it has in its memory. It told us with great certainty that it is Marjoram.