Should UK government recognise foreign polygamous marriages?
No, I do not think any country should accept foreign polygamous marriages and certainly not to provide benefits from taxpayers. If you want to retain your polygamous marriage, remain living in your own country. According to Islam, you are only supposed to have as many wives as you can afford. If that is the case, what the heck are you doing going to the government for support? Therefore, you aren’t even following the dicatates of your own religion! Personally, I think they permitted polygamous marriages so that these old guys could get their jollies screwing young girls. Just like the US, you have a bunch of jerks in government afraid of being seen as racist, so will go along with any crap.
