You can get UK tax relief on traditional 401k/IRA contributions per the US-UK Tax Treaty, provided that you were contributing to the plan before becoming a UK resident. If your employer hasn't arranged for the contributions to come out of your pre-tax (gross) salary, you might need to file a UK tax return at year end in order to claim the tax relief. There are some other threads on this board relating to pension contributions so have a look through the archives.