Well, there's always all those British, non-moslem, men who father children with several other women to keep our side up ! I can think of one white man I know who has fathered 6 children with three women (and he's a solicitor ,so goodness knows what the " lower classes " get up to . I never see them myself, except when I travel my estate to give the workers extra gruel at Christmas)
'But who is 'us'? ' The Kaffur, ie; everyone who aint a muslim. But going on the odds of recent conflicts, they will need 1000,000,000 to have some sort of effect, thank goodness they can't fight there way out of a paper bag.
I think most people want a freeze on non EU recruitment. If there are over 4 millon immigrant workers already here then the families would be 4 times this ie 16 million new faces and 25% of the population is far too many.
Arithmetic is wrong in practice.
There aren't enough women to go round. If there are roughly equal numbers of men and women then the only way each man can have 4 wives is if each woman has 4 husbands.
For each man to have 16 kids each woman must have 16 on average too. Wouldn't happen
If the number of women is constant teh number of children is unlikely to increase much, however many wives a man can have