hi Chocoholic,
First of all take a deep breath, second, tommorow AM, do a search for Specialist US/UK tax lawyers and arrange a meeting with them to discuss your exact standing. I'm not a tax expert, but in ALL of my research for a certain venture I'm wishing to put into effect, the US and UK does have a double taxation treaty meaning you don't pay tax twice. It sounds as though you may need to declare certain aspects in order to be included within that treaty and possibly at worst you'll have to pay a penalty for not sorting it out earlier - maybe by declaring domicile it means you don't pay double tax (guya & lizzit will know more ! wait to see what those clever ones say!)
Your payslip will show that Income Tax and NI contributions (pension contributions etc if you've opted for them) will already have been deducted - so you've already paid those. VAT is included within the price you see when spending, so in effect, you've already paid that. Council tax is the one you'll need to fork out from your net pay. As for the new Green taxes, they'll be included into the cost of things, so won't be a separate outgoing from your net pay. That from your posting leaves PA State income tax, and pending the outcome of what the UK/USA tax lawyers say/do I think eventually, you won't have to pay that - reason I say, is that plenty of other posters here have mentioned the equivalent of $80,000 is what you'll need to be making before having to pay tax over in the US - so if your below that, you should be ok.
Please don't take that last little bit as accurate, I'm not an expert - see what the experts say in your situation and I think you should be able to relax a tad and not burst into tears! I also suggest a nice shot of Whisky/ bourbon/ G&T or whatever your fave tipple is !
Hope this helps a bit!
cheers DtM, West London & Slough UK!