Olives and bananas thrive among the heather in warming Scotland

They have long been known for their luxuriant thistles, abundant heather and the most aggressive midges in northern Europe. But a more exotic future lies in wait for Scottish gardens, according to a major study by plant experts.

Banana trees, olives and other heat-loving species can now survive as far north as Glasgow, they have concluded - further evidence that our climate is slowly but perceptibly getting warmer.

It is a long way from the Victorian era - the period when Britain's taste for exotic plants took hold. Then, wealthy plant collectors built high-roofed glasshouses so their most prized palms could escape the cold winds, frosts and snow of winter.

Even as far north as Manchester plant lovers can recreate the arid deserts of Mexico with blue fan palms and the spiky succulent agave cactus or evoke a sun-scorched Tuscan hillside with olive trees.

In a year-long study, Gardening Which? magazine conducted the first UK-wide trials to test how tropical and exotic plants survived the winter, and uncovered further strong evidence about the shift in Britain's climate.

It involved planting a dozen different exotic and tropical plants in gardens at five different sites across the country, from Dorchester in Dorset to Glasgow, 370 miles to the north. And for many plants, said Rose Ward, the magazine's managing editor and a specialist in climate change, there were some startling results.

"The survival of all of the olives without any kind of damage to them was pretty surprising because olives are so much associated with the idea of the Mediterranean and that sun-baked earth. In Glasgow, they seem to have come through perfectly happily. With the agave, I would never have believed they could get through the winter at all. They look so succulent and juicy. They're Mexican, so what are they doing in a suburban garden?"

Many of the plants tested, such as Canary Island date palm and the chusan palm, are already a common sight around the coastal "English Riviera" towns of Dorset and Devon. Over the past 50 years, average British temperatures have gone up by as much as 1.5 degrees C, and winter temperatures by as much as 1 degree C.

So now, said Ms Ward, these plants survive far more happily further north than many gardeners would have believed possible.