Linaria pelisseriana Jersey Toadflax
With a common name like this, you might expect to be one of the special Jersey plants but it hasn't been seen there the 1950s and so I'm not sure whether you can really say it belongs to the British native flora.
Here in the south Mediterranean it is not uncommon but perhaps easily missed. It is both small, thin and delicate and with the profusion of other Spring plants to behold, the focus of the botanist's eye is easily taken away from relatively insignificant plants like this.