Did I do anything wong when making fries? I bought these Maris Piper potatoes. In the instructions for deep fry to make chips, it says put in a bowl of water for 30 minutes to remove starch, dry, then fry for 6-9 minutes.

I did so however when eating the potatoes they tasted a bit sweet on the inside. I'm not sure but does this mean the inside wasn't cooked properly? 

Usually I believe you need to boil potatoes before frying. Since it didn't say to do this I didn't, would that have caused the result?

The outside layer was quite brown and I think I left it in too long(9 minutes). I also only left it in the bowl for 15 minutes to remove starch.

Does anyone know if I did anything wrong besides maybe leaving it too long which made the outer layer brown?  Does the sweet tasting inside mean anything?  To be honest, the end result tasted like the sweetest chips. I never really experienced it like that before so I'm guessing I did something wrong?
I haven't noticed regular potatoes being sweet when overcooked, undercooked, or even raw. So I don't think the sweetness was due to cooking time. 

However, according to  

http://www.finecooking.com/article/the-science-of-cooking-potatoes-2 

(and many other places on the internet), potatoes stored in the refrigerator will turn sweet as their starches convert to sugars at the cold temperatures.

Is it possible you kept these potatoes in your fridge for a significant time after purchasing them, or maybe they were kept refrigerated at Tesco for a while before you got them? If so that could explain it. I routinely keep my potatoes in the fridge, and when they go sweet, it's really noticeable. I happen to like them OK that way, but they are really quite a bit sweeter than you would expect.