Apologies but I can't seem to find a definitive answer to this.
I've just purchased a Panasonic hcv750 camcorder which records 50p MP4 @ 50Mbs. In the past I have always shot at 50i or 25p with shutter speed of 1/50 in accordance with the 180 degrees rule. I therefore assume for 50p I should use a shutter speed of 1/100 for normal recording (I'm not interested in slow mo).

My main output will be to blu ray which I believe doesn't accept 50p. I have therefore been using a 50i template in Sony Vegas for the 50p footage. I assume Sony Vegas just disregards every other frame to give 25f/s.

I have recorded using 50p @ 1/50 and 50p @ 1/100. When I review the blu ray footage the 50p @ 1/50 looks more natural which is not what I was expecting. The 1/100 footage looks like 50i @ 1/100 in terms of the motion blur or lack of. Is this because of the conversion to 25f/s for the blu ray, so 1/50 shutter speed should be used ?
My conclusion therefore appears to be:
For blu ray 50i shoot at 1/50.
For internet, PC or other 50p capable device shoot at 1/100.
Is this correct? Advice would be greatly appreciated.

I'm not shooting or presenting at these framerates & speeds, but your math and conclusions check out to me.

A 1/50th-ish shutter speed for what presents as 24 or 25fps is the important element that determines motion treatment; sounds right to me!

1/100 shutter begins to APPROACH "stopping power" of typical motion with little motion blur so I would tend to avoid it for organic looking motion. By the time you get to 1/125 it becomes noticeable.

I think you are correct in using 1/50 for natural motion on 50P regardless. I would only go to 1/100 if the camera didn't have a 1/50 setting or I wanted a strobing look, was desperate for shallower depth of field or I wanted to slow the footage down. This is the advice I would give if using 30p or 24P as well. Those frame rates benefit from a 180 degree shutter as 1/30 and 1/24th are too slow and blurry for my tastes.