The mild weather has led to an early surge in the signs of spring, with snowdrops and hazel flowering and elders starting to burst into leaf, wildlife experts have said.
There have even been sightings of ladybirds and butterflies, according to reports from the public submitted to the Woodland Trust's nature's calendar project, which monitors the changing seasons.
Such signs of spring in January have become more common over the last decade and may point to spring arriving earlier than in the past, the Trust said.
But species which are fooled into early activity as a result of the mild weather, such as frogs which might start breeding or trees blossoming, could be vulnerable to freezing conditions which are not uncommon in February or March.
In the first two weeks of January there have been 31 reports of snowdrops in sites ranging from Kent to Anglesey, 44 observations of hazel flowering from Devon to Lincolnshire and 13 sightings of elder buds bursting.
There have been two ladybird sightings, in Darlington and Crediton in Devon, two records of small tortoiseshell butterflies have come in from Ely and Pembrokeshire, and one red admiral has been spotted in Crewe.
Dr Kate Lewthwaite, Woodland Trust nature's calendar project manager, said: "People may be surprised to see such spring-like activity in January but Woodland Trust data confirms that it has become more and more common over the last decade or so.
"What this highlights is the importance of having diverse, inter-connected habitats which allow species to react to any changes in climate and adjust accordingly.
"With habitats coming under ever greater threat and fragmentation, the pressure on our native flora and fauna will only increase."
The Woodland Trust is urging the Government to increase protection for ancient woodland in England to help the many species which rely on it for survival.
Matthew Oates from the National Trust, said "proper" winter weather with cold temperatures was needed soon, or wildlife would be fooled into thinking it was spring and could then be caught out later in the season by a cold snap.
"There is real danger that the year will launch into another very early spring; and an early spring usually ends in tears," he said.
He added that "i f it wasn't for the incessant rain, spring would be romping ahead" but plants had been slowed down by saturated conditions. Both people and nature had had enough of the rain, he said.
Dr Lewthwaite said climate scientists were predicting more "stop-start" springs, in which the UK could see very mild conditions in January and then a return to more typical weather later in the season.
And she warned that the UK had a highly fragmented landscape which made it hard for species to adapt to changes in the climate, for example by making it difficult to move to more suitable areas.
"We're making it harder for our wildlife by cutting our natural habitat into smaller and smaller pieces," she warned.
Along with efforts to tackle carbon emissions such as improving energy efficiency, there was a need to make the landscape more interconnected by linking up habitat to give wildlife a better chance to move and adapt to climate change, she said.