Butterflies such as the orange tip and holly blue usually appear in May but were seen last month. The red admiral is now seen in January and February instead of May.

Oaks and ashes are leafing earlier and sandmartins were spotted in Britain last month. They usually return from just below the Sahara in April. There were also an unprecedented 4,000 sightings of bumble bees in January.

Tim Sparks and Nick Collinson, of the UK Phenology Network, which studies the timing of natural events, produced the report, published in the latest edition of BBC Wildlife magazine. It suggests that spring starts roughly six days earlier for every one degree Celsius rise in temperature.

There is also a four-week difference generally between the South West and the north of Scotland. Taking March 21 as the traditional start of spring is therefore largely irrelevant to the natural world.

The researchers, who collated 300 years of records, say that the changes in Britain’s seasons have far-reaching consequences for native wildlife. Frog spawning, for example, which has taken place just before Christmas for years in milder parts of Cornwall, is happening as early as October, even in Northern Ireland.

The flowering of daffodils and white dead-nettles was seen on Christmas Day last year, and people in Scotland now cut their grass in winter.

Warmer temperatures, shifting patterns of rainfall, higher sea levels and more extreme weather could lead to the disappearance of beech woods in the South of England and drive out mountain species that thrive in a cold environment such as the capercaillie and the snow bunting and a number of arctic alpine flowers seen in the Scottish highlands.

The findings are not all gloomy because warmer temperatures are attracting foreign animal and plant species. Birds such as the black kite, the cattle egret and the hoopoe are travelling farther north from southern Europe.

Moths such as the flame brocade and the Spanish carpet are seen in the Channel Islands and are expected soon on the mainland. Two butterflies absent from Britain at present, the black-veined white and the mazarine blue, also are expected to return.

A new plant species already in the Channel Island and is now seen in the South of England is the water bent. Experts also expect the water primrose and bay to establish on the mainland. Other species moving northwards include crickets such as the long-winged conehead, and gatekeeper, comma and speckled wood butterflies.

Dr Sparks said: “There has been a steady, almost stealthy, change to the start of spring. It has crept up on us but we have got used to it.

“We have now so got used to mild winters that when we get a cold snap we think it is really cold — in fact, it is average temperature for winter. We have forgotten what cold weather is really like.”

The authors of in the article said: “Climate change will affect our wildlife, but nature is difficult to predict. What is clear is that we need to act now if we are to help the natural world to survive and adapt to future change.”

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