Throughout the series US secret service agents operating in the UK are shown using firearms. This is inaccurate armed security for foreign dignitaries and diplomats including the US president is provided by the Metropolitan Police's Parliamentary and Diplomatic Protection branch. The UK's strict gun laws prevent anyone except UK police officers using handguns or assault weapons in Great Britain.
Several of the cars in the Moscow location scenes have the steering wheel on the right side. Indicating that it the scenes was actually filmed in the UK.
Scenes are set back-to-back in London, Chernobyl, America, with no apparent time taken for international travel, nor difficulties in getting through security every single time.