Look up per diem reimbursement rates and mileage deductions for business travel worldwide.

Complete
United States → London, Greater London, England, United Kingdom
Item Name Destination Amount Conditions
Lodging London, United Kingdom 424 USD per night State Department DSSR 920 footnote 13: The term "London" is limited to the area falling within the City and 32 boroughs (including Heathrow Airport), which together are known as Greater London.
Meals and incidentals London, United Kingdom 174 USD per day State Department DSSR 920 footnote 13: The term "London" is limited to the area falling within the City and 32 boroughs (including Heathrow Airport), which together are known as Greater London.

Source URL:
https://allowances.state.gov/web920/per_diem.asp
This source provides official travel rate information from allowances.state.gov.