I agree with all of those who have posted, that it is quite acceptable here to take a career break. (Although it may well vary by industry.) I actually think it is much more of a disadvantage to be married and in your 30s but not have any children, because the employers will be worried about having to give you maternity leave. I was looking to change jobs at age 30, and again at 32, and each time every single interviewer asked me if I was planning to have children, and was obviously concerned about it. (Of course I lied – and I figured that if they are asking illegal and discriminatory questions, they did not deserve an honest response. And, I did get pregnant soon after starting the second job, but did not mean it to happen so soon!) If you already have the kids, they are somewhat relieved that they do not have to worry about this, especially if you have already taken the career break and gotten that "out of the way".
I took several years off work, and nobody seemed to mind in the least; it was considered quite a legitimate progression. I guess there must be some "macho" jobs where people will not take you seriously because you have young children – but involved fathers can get this too so I think it is more about whether you are willing to give up your personal life for career, rather than specifically about being a parent, in that type of career field.
It's disappointing to read that people are still facing discrimination for not having UK experience. I certainly faced this when I first came over in 1991, and they did not bother to hide it, openly saying things like "of course your Canadian experience wouldn't count", "of course we would not pay you as much as a British person" and so on. I would have figured things had moved beyond this. I'm pretty sure it's not as universal as it once was however, especially if you are in London. The companies I have worked at and contracted at since 2000, and the companies my husband works at, and the client companies I have dealt with, have loads of foreigners, and a number of large companies deliberately recruit foreigners. Again, it must depend on your field and perhaps in the part of the country you are in.
Good luck.