The red variety of clover, Trifolium pratense is in evidence by the hedgerows at the moment.
It is taller, with a larger flower head than white clover. It is grown as a fodder crop and it also fixes nitrogen in the soil, improving it for the next crop.
The main pollinator of red clover is the long tongued bumblebee, Bombus hortorum. A long tongue is required to reach the nectar, although shorter tongued bees have been observed cheating, by biting a hole at the back of the floret.
And of course, if you find one with four leaves you are very lucky indeed.