What whistle was used on Hogwarts express in the Harry potter films?

I believe it to have been that of a Hall Class locomotive. It certainly wasn't that of an engine built stateside.

Yes, typical British "peanut" whistle. The Brits wouldn't recognize our beloved multi-chime whistles.

They use a Hall-class locomotive in the films, not a Castle-class locomotive, so the whistle sounds like this.

The thing about the whistle used in the Harry Potter films is that, at least to me, it doesn't necessarily sound like most British whistles. Yes, it's very similar, with it being very high pitched, but most of those whistles sound like just one note, where as the Hogwarts whistle sounds like at least two different notes. I've heard it could be a Cosby 3 chime, short bell of some sort, but I'm not so sure about that.

Hogwarts Express' locomotive is Olton Hall, formerly a Great Western 4900 Class locomotive.  The West Coast Railway Company owns her now, and is now temporarily on display as part of a Harry Potter exhibit in the UK.  She is in running order, and the trip you can ride on the West Coast Railway is the route used in the movies, including riding on the coaches used!

Polar Express 1225 is correct: it uses a Crosby Tritone Whistle, which was also in use on other UK locomotives such as the Gresley A4 Pacifics (like Mallard).

I am nearly positive that the sound in the film is foley and added in later in post production. The sound is probably whatever the sound designer wanted to plug in.

I actually saw a video of a Greeley a4 locomotive and it's whistle was nearly identical to the Hogwarts whistle from the films, only difference i could make out was maybe the film whistle was a bit higher pitched but not by much.

the whistle used is not of the engine used the whistle used is a 3 Chime whistle that belongs to Brittania Class 70013 Oliver Cromwell this will have been recorded and added in the edit here is the engine in question