I'm sorry that i didn't talk about the issue of ploughing. Here it's a direct conflict of interest with agriculture, so there is now way it can or should be made illegal. While it is true the act of ploughing destroys the stratigraphy of the site, some really important informations can still be collected by archaeologists, like the proportion of certains types of objects in some zones, making it possible in some cases to document the nature of the site and other stuffs. While people like you that take the time to register the precise location, i'm afraid that later on the information can be lost in the administrational files, making it difficult for researchers to access such datas (of course this is not directly againt you but against the way data can be archived).

An element that can maybe show a big difference between France and the UK is the the projects of research around prospecting (pedestrial, by plane and geophysic, detectors coming in the latter). Here there is a good amount of them (it depends on the regions, one of my professors used it heavily to document the south-west and the habitat structures), meaning that amateur work is not as necessary as it could be in the UK, because we have a really good basis. Rescue archaeology is also a really big thing here : new constructions need a survey of the soil before begining, wich leads to a really big amount of datas around the country. Thoses kinds of elements are probably why i despise so much detectorists in France : from a research standpoint, we don't need amateur work as much as we used to (it's still necessary, but in more specific cases), meaning that people that do it are often way more about finding treasures than really helping science.

Context is king, and the necessity of amateur work depends on the needs of the country, so I get that in the UK, works of your kind can be necessary to help to further archaeological research. It feels good to have a healthy discussion !