Our woods offer the best places to witness spectacular displays of bluebells. And after reports of spring appearing earlier in Norfolk each year, the blue woodland carpet should be out in force come April.

For a few short weeks, before the leaves begin to unfurl, our woodlands are transformed into a hypnotic blue wonderland.

From afar it can appear as though the oaks, beech and ash trees have been wreathed in a purple mist as waves of bluebells flower in unison to provide one of the most spectacular floral displays in the world.

Spring bluebells have inspired some of our greatest poets and our most cunning plant thieves, they thrive on our isles like nowhere else and quite rightly are our national flower.

The appearance of the bluebell is a traditional harbinger of spring, symbolising the change of the seasons and of the summer's warmth to come.

Bluebells chose to flower at this time of year so they can take advantage of an ecological niche. Trees' leaves are yet to emerge meaning more sunlight gets through to the plants on the woodland floor.

The plants are early starters, making sure they are flowering before more temperature-dependant species are in bloom.

The canny bluebells burst into bloom around mid-April, with their sticky nectar attracting the first of the year's bumblebees who helpfully pollinate the flowers.

But all too soon the spectacle is over as trees unfurl their leaves to steal all the sunshine.

To take advantage of the blue bloom the National Trust is this year operating a bluebell watch which reveals when flowers are coming into bloom on its properties up and down the UK.

Ian Wright, garden advisor at the National Trust, whose woodlands at Blickling and Sheringham Park are two of the best places in Norfolk to see bluebells in all their glory, explains: 'England without bluebells? It would be like cancelling spring and going straight to summer. Can anything actually beat walking through a bluebell wood on a warm spring day with all your senses in total overdrive? But for the bluebell, that time of glory is the commutation of months of preparation, much of it going on unseen.

'The bluebell starts to grow in the late summer, hidden away underground, its clock ticking towards spring. The bluebell's sole aim is to set its flowers before other plants that are more temperature dependant can compete, and before the tree canopy above shades out the forest floor.'

Bluebells are slow to establish themselves, so finding large clumps of the flowers is a good indicator that you are in ancient woodland.

But despite being protected by law they are under threat, both from habitat loss, foreign rivals and unscrupulous collectors who dig up the bulbs to sell on for profit.

The Spanish bluebell began to invade and compete for space with our British native 250 years ago. It poses a threat as the plant can interbreed with the UK flower.

Mr Wright explains: 'You would be mistaken if you thought this iconic plant of spring is untouchable. It faces real challenges in the form of climate change which may give other plants a chance to compete at the same time or even losing its unique identity by hybridising with its invasive Spanish cousin.

'But for all this, the bluebell remains one of our real champions of spring, so I urge you to make the effort to go and visit a wood near you, and stand still in awe at nature's sheer beauty.'

An easy way of telling a Spanish from an English bluebell is the English plant bares drooping flowers one side of the stem and is scented, while the Spanish bluebell is unscented and has flowers on all sides of the stem with a larger more open bell.

• The National Trust Bluebell Watch can be found here.

• The Natural History Museum's Bluebell Survey can be found here.