Underground lines will be suspended this weekend as engineers begin scheduled summer track replacement.
Transport for London will be starting major work on the Metropolitan and Piccadilly lines through Harrow tomorrow.
There will be no service on the Metropolitan line between Wembley Park and Uxbridge or Northwood while points are replaced at Harrow-on-the-Hill on Saturday July 19 and Sunday July 20.
On the same days and until August 10 there will be no service on the Piccadilly Line from Rayners Lane to Uxbridge.
The work is the start of more than 20 days of closures during the summer months for track replacement around Hillingdon.
TfL says there will be rail replacement busses in operation during the works.