-It's the largest event of its type in the UK and thousands of people are expected to visit central London to see West End performances for free all weekend.
-Performances are programmed on stage 11am-6pm on Sat and 12pm-6pm on Sun.
-Entry is on a first come, first served basis.
More top news
More than a tenth of the Piccadilly Line train fleet is out of action because of emergency repairs to damaged wheels.
Rows of students stood and turned their backs before filing out of the lecture theatre.
Effie the endangered Western lowland gorilla has given birth to a healthy baby boy at London Zoo.