Hi! I'm in Year 13 at the moment and I've applied for various linguistics courses. I can't tell you what it would be like to actually study them, but I can tell you what I think based on the offer holder days and open days that I've been to, and the students that I've talked to.
As far as I can tell, the difference between ELL and L courses seems to be quite minimal. ELL of course focuses more heavily on English - for instance, if you were doing a module on syntax, it would likely focus more on the syntax of English than on syntax as a whole. ELL courses also tend to have more modules available on the history of English, or on global varieties of English, rather than on the building blocks of language, such as phonetics, morphology, etc.
What I struggled with when applying is the fact that most universities won't offer an ELL course and a Linguistics course, but only one or the other. This means that the courses that I applied to all have different names at each different university, but they are functionally all linguistics courses. I have also noticed that ELL courses don't seem to be treated like joint honours courses by the majority of universities, likely because of the fact that the university would only offer ELL and not Linguistics as well as this. At ELL-only universities, the ELL course tends to exist entirely within whatever department houses Linguistics - you wouldn't be splitting your time between multiple departments and multiple courses. For instance, the Warwick 'English Language and Linguistics' course is the only option to study Linguistics without taking a modern language, and it functions just as a Linguistics course at any other university would, only with a stronger focus on English.
Rather than thinking about the title of the course, I spent a lot of time thinking about the modules offered at each university, and I would encourage you to do this too. For example, Warwick seems to be very strong at teaching communications (eg. business communications, discourse analysis), whereas Lancaster is building a reputation for excellence in corpus and forensic linguistics. York is also highly respected for corpus linguistics (as far as I can remember - this wasn't one that I visited myself!). I would strongly encourage you to think about what areas of linguistics you are interested in, search for modules that match these areas, and then ask lecturers about the specialist areas of the university when you visit for open days, because they may give you different answers to what you have heard elsewhere.
Good luck, and I hope you find the right course for you!