They immediately reply in English and have little tolerance for someone speaking their language with even a vague accent.

Have seen it many times.

As a Finn, I'd interprete this as trying to be helpful, and less about not tolerating accent. "Oh, they're struggling with Finnish, it's easier for all of us if I switch to English." In my opinion, this is one of the top reasons for difficulties in learning Finnish - it's difficult to get the Finns talk Finnish with you. One has to insist.

Interesting. Is this professional conversations or in stores / restaurants / on the streets? I thought English is not spoken by many folks over there, at least outside the IT/tech scene.

If you pick an average person under 40 they will have near-perfect English. Partly due to media, partly due to the internet.

English seems common in the groups of immigrants you come across too. I know people who've moved from France, etc, and there are lots of immigrants from various countries - many of whom speak their own language, and English as the second. Some go on to learn Finnish to a greater or lesser extent.

I've ordered food in restaurants, cider/whisky in pubs, etc, and had the server just reply back in English.

Me: "saisinko omena cidre?" Them: "Do you want ice?"

On the one hand it is helpful at times, but on the other hand it is deeply frustrating. 90% of the staff at the local newsagents has pulled me aside on a quiet morning and asked "Do you prefer English or Finnish?" I say "Finnish", but to be honest the conversations I have with the shop-staff are mostly them reading the total, and asking "would you like a receipt/bag/anything else?" so it doesn't help me in any real sense, but it's nice they offer/ask.

I think if you tell people you want to practice your Finnish, and you're not in a busy restaurant / grocery store, they'll entertain you. Younger Finns just have stopped assuming that people would bother learning Finnish.

My experience at the store/ when ordering drinks has been that I'd get the replies more often than not in Finnish and had to switch to English myself when it was something that I didn't understand. Key is to get the pronunciation right - which is far easier as a German.

And yes, younger people know English well and will usually switch to English if you're struggling - unless they think that their English is too bad (which it usually isn't).

Alcohol is very expensive though!