The rules are somewhat complex.The nature of your work and the basis on which you are in the UK will play onto this.First, as a US citizen you will definitely be taxed by and have a filing requirement with the US. The amount you owe may be zero, but you only know that at the end of the process.If you are visiting (but visited a lot) but were working primarily for your US employer (say you were overseeing the training of a UK based team - not doing the training), then you would not normally be taxed by the UK.However, if you were actually doing work and being paid by a UK company, then you will have arrived on some sort of work Visa and that will have defined the nature of your UK tax obligations.As an example a US citizen actor filming for 60 days in the UK will pay UK income tax on the income associated with that filming (both immediate and long term), will not get the foreign income exclusion because they are normally resident in the US but will be able to take the UK tax paid as a credit against the US tax assessed on the same income.