Why do we expect to buy tomatoes and cucumbers all year round?

When did it become an inalienable human right for 65 million Britons to have a cucumber in March? When did we suddenly regard the possession, weekly, of a half kilo or so of vine-ripened tomatoes as fundamental to our very being, when our corner of the northern hemisphere is still essentially frozen and has been for months? If we were in southern Italy or if London were transposed with Madrid – so 800 miles closer to the equator – then one might begin to think that a leafy salad or a few tomatoes could or should be a daily staple, even in these darker days. But up here, at 52