Factual error: When Debra Messing and Dermot Mulroney 1st arrive in London Debra goes to a pub to change her outfit, the shot showing the outside of the pub you can see an American style traffic lights eg walk, don't walk which are nothing like the English green man red man traffic lights.
Factual error: Kat goes to multiple ATMs to withdraw money, since the limit on machines in the UK at the time was £250. However, that limit is for withdrawals from one account in one day, not from individual ATM machines. You can take as much as you want from your accounts in person at the bank, but not from machines. It's ridiculous to think she would've had enough different accounts to only take £250 from each but return with thousands.
Factual error: When they are leaving the USA to fly to London and are checking in at the airport, a guy walks past in an Easyjet ground handler's uniform. Easyjet doesn't operate in the USA - clearly filmed in London Gatwick airport.
