I find it amazing that such a simple question gets so many answers, some contradictory.
I think it a serious indictment of the whole regime that basic information like this is so hard to get hold of. Yes, you can read though the CAP/EASA blurb but after a while all you get is a headache as you are bounced around between regulations. Even instructors/examiners don’t always get it right (whatever right is) and I would venture that there are some posting in this thread.
My (probably erroneous) take on it is that “50hrs cross-country” is what it says, no more, no less. You don’t have to do it in anything other than an aeroplane in which you could log hours for a PPL(A): no need for IFR, twins, jumbo jets or rocket-powered hovercraft...