This is just a bit of info that will be irrelevant to most of you, but hopefully very very useful for a small number of people who stumble across this post.
US citizens working in the UK for a US company, or a US owned subsidiary, or a company that can be proved as being controlled by a US company, are covered by many aspects of US employment law, particularly on matters involving discrimination on basis of gender, disability, race, etc, etc.
This means that you have the option to pursue your employers through the UK system or the US system. The remedies in the US are much better, and the whole system is far more pro-employee than the UK system. If you have the luxury of choice, consider using the US system to pursue your UK employers.
It doesn't matter if you are a local hire, on a local contract, it doesn't matter if you are only a US citizen because your parent is a US citizen, and you haven't even gotten around to getting a passport.
This is not widely known, even among UK employment solicitors but is explicitly legislated for by US congress.
My husband has suffered some pretty blatant disability discrimination of over the last 12 months. His old company was expecting us to sue in the UK, but have shat themselves with surprise after being informed they were being sued in the US, where settlement figures are roughly 10 times the size of settlement figures in the UK. Yep, they had plenty of chances to fix things, screw them.
Interestingly it creates the strange situation where US citizens effectively have more employment rights than their UK citizen colleagues working on the next desk. I've often thought of what would happen if after a US citizen claimed rights available to them under US laws, and then a UK citizen colleague claims those rights in the UK, as it would be racially discriminatory for the rights to be only offered to US citizens. A sort of legal domino effect, or at least a lawyer's hornets nest.