bugs on mint plant

Hi, this is my second year of growing my own salad and veg, this year i've moved upto a 8 x 6 green house and so far everything is growing quickly. My issue is, this morning i went into the greenhouse and discovered on my mint plant hundreds of little green lumps all up the stems, are these green fly waiting to hatch out??

No - greenfly are born live!

You can wash greenfly off with mildly soapy water, but they will come back - they are a major pest in greenhouses in winter, as there are few predators.