There is a common misleading statement that ragwort is an "injurious weed" so it is dangerous.
The confusion here comes from the use of some rather peculiar terminology in the Weeds Act 1959. It used the word "Injurious" to describe a range of weeds only one of which is actually poisonous. There is confusion in many people's minds with the word "Injury".
To understand this you have to understand the origin of the word. It actually comes from the Latin word "iniurius" which in medieval Latin would have been spelled "injurius" . It means unjust or wrongful. From this it was extended to something that did injustice or wrong to something else, or that did harm to an interest.
Injury is another derivation which comes from the same basic word. It originally meant a wrong done to someone and the meaning of "wound" is a secondary derivation.
Injurious weeds are weeds that are considered bad for the interests of agriculture. It doesn't mean poisonous or that they injure something, some of them are actually edible.
The accepted best source for the meaning of English words is The Oxford English Dictionary as it is the largest, most comprehensive and most detailed dictionary of English and this is what it says for Injurious:-
1. Wrongful; hurtful or prejudicial to the rights of another; wilfully inflicting injury or wrong.
2. Wilfully hurtful or offensive in language; contumelious, insulting; calumnious. (Now only of words or speech, and passing into sense 3.)
3. Tending to hurt or damage; hurtful, harmful, detrimental, deleterious.
It is very clear that parliament meant that meaning of harmful or prejudicial to the interests of agriculture because of the language used when it was discussed. The Weeds Act was a consolidation act that replaced earlier legislation and was not subject to discussion in parliament but the words "injurious weed" were first introduced in an amendment to the Corn Production Act 1917 which was debated as part of the Agriculture Act 1920 on the 3rd November 1920. There are many uses of the words "injurious" and "injuriously" during the debate. All of them have the "harmful/prejudicial to interests" meaning including this from James Gardiner then MP for Kinross and Western Perthshire.
"Every agricultural committee I know has intimate knowledge of agriculture and an intimate knowledge of the district in which control is to be exercised. They are, therefore, well able to ensure that nothing injurious to the cultivation or the country results from the orders they give. "
It is very clear that the meaning of the word as used in this legislation is not "Toxic" or "poisonous" but harmful to the interests of land or agriculture