Original post by MeduseSalut.
So, the good thing is that you do actually have an advantage having been exposed to the language. You have some past knowledge that will have remained, but you essentially need to 'resurrect' the vocabulary and structures which you have forgotten. More exposure is key to this. A grade 8 a GCSE is a good start, but obviously, it's some way away from where you hope to be in the future. Your approach to language learning really doesn't need to be all that different, except that you need to identify your current level and where you need to improve most. You need to gather a bunch of good quality resources (either online or in person) to start learning again. A tutor (depending on whether you can afford it) may be a beneficial. If not, you can by all means take online courses or just try self-teaching with textbooks and exposure to French materials (i.e. podcasts, books, news articles, online/offline content). Make note of any new vocaulary/idioms that you come across - either write them down in a notebook, an online document, or you can create flashcards on Quizlet (recommend). If you're going to use an online dictionary, I'd suggest WordReference. LawlessFrench is a really great website for explaining grammatical concepts, providing vocab lists and some other great resources.
Babbel and Duolingo are fairly similar. Of the two, I'd say Babbel is the best. However, both are quite limiting if you do not have a paid subscription. They are good for a beginner-nearly intermediate learner, but after that point, you may find the exercises getting a bit repetitive or basic. I used both at GCSE level, but never stuck with it and did fine with just a textbook and lessons. If you are going to spend your money regularly, I think it's more valuable to invest in a tutor instead. By all means, keep using the textbooks you already own if they suit your level.
You are going to need motivation. Anyone needs this when learning a language, regardless of what level they're at. You have a goal (working in Paris) and this can be a great source of motivation. Pinning up pictures on your bedroom wall or by your desk can be a nice reminder to keep progressing. Also, consider why you 'lost' the language and how you are going to ensure that you stay consistent.
It appears you have some anxiety and perhaps some shame that revolves around making mistakes, fluent speakers correcting you and switching to English. This is really just a matter of acceptance. You can only control your learning and your actions. If you make the odd mistake, it really isn't a big deal. Every language learner makes mistakes. It's inevitable. You won't know what you're capable of if you don't try. If someone switches to English (which has happened once to me when I was working in Lille), it's not the end of the world. If it's a stranger, don't worry about it. If it's someone you're going to be speaking to often/working beside/getting to know better, you can ask them to continue the conversation in French so that you can progress. Ignore biased/rude people if they want to be picky about your accent. Accents are wonderful things and shouldn't be used to discriminate. The fact you are trying to learn a language shows your dedication and this shouldn't be overshadowed by something as superficial as an accent.
I am not familiar with UCL so I'm not sure whether or not they will have French internships, however, you can always contact the languages department and ask them to notify you of any language-focused activities that are accessible to non-language students. There may also be a French/languge society you can join up to. It's certainly worth looking into.
Essentially, I advise that you take some sort of proficiency test to establish your level and then to go from there with any resources you can get your hands on. Create a plan around your weekly routine and stick to it. You of all people will know that language learning requires consistent bursts of effort.
If you have any more questions or need some advice, feel free to respond here whenever.
Bonne chance !