Originally I had one tiny Yellow Toadflax plant but although I like it, I am continually removing the new shoots and creeping roots because it can be very invasive.  Common or Yellow Toadflax (Linaria vulgaris) is a common plant of waste ground, road and railway verges and hedges and was believed to have been introduced to UK as a garden plant.   Its flowers which are like garden Snapdragons, are yellow with long spurs and have orange centres on the lower lip acting as a landing pad for pollinating insects.  Apparently it is an old country custom in parts of Sweden to put Toadflax flowers in milk, and stand the infusion in places where flies are a problem.