Good post. You brought some good points. Firstly his wife of 20 years imagine put just as much effort into their marriage so really 50/50 is fair. I gave my wife 75% as I didn't want her working like a dog into her 70s.

Don't think it's 50/50 for everyone. It isn't. It goes by time together. ..whether there's children. ..what did the wife brought to the table if anything and what contributions she's made over the time spent living together as man and wife in the UK.
Some think it's easy to marry a British come over here divorce him and take half which morally isn't her's.
For a start, the time spent together as man and wife starts from when the wife get ILR for example for a Filipina who's been here 5 years They may get between 1 and 2% of his pension pot. That doesn't sound alot but if the pot is big which they generally are 1% of an average 250000 is a tidy some. Better than nothing. It's certainly well short of the 50/50 the 20 year wife got. ..rightly so.

As pointed out, pre nups are not legally binding. So as the law stands, it's a worthless exercise.