It is not easy to answer, except to say, that if you follow Twitter there are many signs. The BBC's Springwatch has been receiving tweets from all over the UK on the topic.
On Feb 2, lakedistrictnpa tweeted from Kendal:
Saw loads of snowdrops on the walk into work. Spring’s a-coming! #ukspring
On Feb 4, Boudica_ tweeted from Devon:
Red-tailed bumblebee spotted yesterday in Herts; recorded @#naturescalendar.
On Feb 6, jerembybiggs tweeted:
Is this the UKs first frog spawn?: http:wp.me/pjz4j-1oe
On Feb 8, landguardranger tweeted from Felixstowe:
just seen first elder leaves breaking their buds on reserve, bliss #ukspring is on its way.
On Feb 10 Jemnick tweeted from Hampshire:
Chaffinch, song thrush, dunnock all in spring song mode! Great! #ukspring
On Feb 20 skylarksue commented on BBC’s Nature UK blog
Here in Essex garden, snowdrops have been out for 3 weeks. Bluetits are rearranging grass & straw in the nestbox. There are buds on my cherry tree.
Meanwhile, this blogger, writing from Boston, has just been cross-country skiing. The record-breaking snow is beginning to melt. Houses on the sunny side of the street have a foot still in their front yards; those on the shady side have two-to-three feet.
To record your own Spring sightings, sign up to nature's calendar
To follow Spring's advance in the US, look at Journey North 2011
To follow the way a school has followed the first signs of spring, year after year:
school postcard asks our snow-bound co-editor to keep an eye out for the first daffodil
flowers on stage: snake's head fritillaries