How important is the right grammar for you?
English speakers don't really care, we can still understand what you are saying. We are so used to errors. Especially me coming from places like Chicago and Detroit. The fact you type that paragraph shows your English is on point. That's such an accomplishment!
With much of the world learning English as a second language for commerce, science and travel, and with large immigrant populations in the U.S., we're quite used to hearing imperfect English, and I'd say that we're quite tolerant of foreign accents and grammatical slips as long as it can be understood. I'd assume it's the same in the U.K., though I've never been there. (We won't count one afternoon in Northern Ireland. :^) Definitely do work on areas needing improvement, but don't be self-concious.
The spoken word is ephemeral but the written word is eternal, as are written mistakes. I agree that good grammar is more critical in writing, especially formal documents and correspondence. But the little bit of your writing that I've seen looks very good. Fortunately there is usually plenty of time to review and revise writing, unlike unscripted speaking. Even when writing my native language, like right now, I review and revise many times before posting (and I usually still find something to fix immediately after posting.)
Don't worry too much about it. Your mistake here doesn't cause any confusion or misunderstandings, so it shouldn't get you in trouble. The main causes for miscommunication are usually related to vocabulary and pronunciation. I don't mean having a German accent, but I mean having wildly incorrect stress patterns, unclear articulation of final consonants, and improper vowel length. I would say that your tone can also cause miscommunications, making your listener think you're being arrogant or condescending. This often happens when foreigners keep low intonation constant. Native English speakers probably don't consciously notice these things, but they lead to the most miscommunications, even among native speakers. I don't think you'll sound stupid at all, but I would say that you should be prepared for someone to be a bit guarded about some of your comments due to your tone. I don't know how you speak, but I think Germans often get misunderstood as arrogant in many cases because of the knee-jerk reaction that native speakers have to intonation at particular times. For my perceived notions of German work/study culture (very limited), which is very "low-context" and literal, this difference in culture can sometimes be off-putting (I'm also not a Brit though). You may also notice that tone makes a lot of English native speakers upset about customer service when they travel abroad to other countries... I always feel bad when I see these situations. This falls under that category of you seem proficient enough to know the nuance, but it's quite a subtle thing that is hard to truly master.
It's not the topic of the post but how are you going to get access to a British university under Brexit conditions when all the Erasmus students have to leave Britain?
I am German, too. I try to iron out the typical mistakes Germans make when they speak English but I, too, would advocate not worrying too much, like ericb100 already said. Your English will improve massively anyway once you are surrounded by people speaking it.
Talking about Germany: I work in a hospital, and among the doctors here there are many immigrants. Typically when I talk to them, I notice the mistakes they make much less than when I read the medical letters they write. I guess English native speakers will have an experience not too different from mine.
That's a great point Diotallevi on the writing side. While I think grammar mistakes in spoken language are easy to look over, if they are in writing, in a formal letter or document, it's much more egregious. Mostly because one should run spellchecker and grammar checker and those hopefully point out those items. If it's an informal email to a colleague, or message board comment (I'm guilty myself in my native language!) then mistakes will be much more likely and tolerated.
I wouldn't worry too much. Obviously without hearing you I don't know what grammatical mistakes you're making, but the important point is that people understand you. More often than not a native is going to know what you are talking about and even if you're getting tenses wrong or adding or subtracting things that should be there, a native is not terribly worried if you're grammar is not perfect.
I'm not certain if business may require more perfection...it may depend on what aspect of business it is? If you are preparing business documentation or contracts then there probably would be a lot less tolerance for mistakes, but good old spelling and grammar check can help you there mostly.
I'm in IT and I work with many people who didn't originate in the U.S. They mostly all have grammatical mistakes that they make and many have thick accents. You get used to it. I don't care if they make mistakes as long as I can understand.
All you can do is keep striving to get better. As the business world becomes more global, even in business people are dealing with many people whose first language is not English. So I think this is less of an issue than I would think it would've been a few decades ago.
Those confernce calls with folks from the US, ,the UK, Singapore, Hong Kong, Australia, Germany, and Russia are always fun. It's the guy from Scotland that I can't understand. :)
Haha. One of my friends is Scottish and there are many times I haven't got a clue what he's saying. His wife (my co-worker and friend) says when he's with his Scottish friends she can't understand anything at all.