Following the second warmest winter on record two natural events suggest we have leapfrogged spring and moved straight to summer, a conservation charity said today.

Following a weekend where some parts of the UK basked in temperatures 10C above the seasonal average, the Woodland Trust said flowering hawthorn and the return of migrating swifts indicated that summer had arrived a month earlier than usual this year.

The trust said sightings of hawthorn flowers and swifts, made by the public as part of the Springwatch survey it runs annually with the BBC, suggest climate change is having an impact on the timing of our seasons.

"Spring is the new summer" and "April becomes the new May", a spokesperson said.

Experts from the trust have verified public sightings of hawthorn flowers in hedgerows right across the UK, although typically they are not expected to appear until around May 11.

The sight of swifts flying across the south-east and Gloucestershire over the past few days also suggests the seasons are out of kilter; traditionally the birds return from their migration around May 10.

Dr Kate Lewthwaite of the Woodland Trust said the exceptionally mild start to the year had prompted the early appearance of these traditional signals of summer.

"The timing of the seasons is changing in length and complexity, with the mild winter and warm spring contributing to warmer than average temperatures," she said.

"It is an example of how climate change is affecting our wildlife and seasons."

The importance of hawthorn blossom as a harbinger of summer goes back to ancient times. The tree is known as the Queen of the May and was at the centre of the traditional custom of "going a-maying", whereby branches of the plant were cut down to adorn doorways and protect homes from evil spirits.

This happened on May Day, which prior to 1732 was celebrated on May 13.

Scientists at Kew Gardens have also noted the affect of climate change on UK plants. They have been monitoring 100 species and have seen that almost all of them have started to flower and fruit early, some by more than a month.