Conservative Assembly members criticised the move on twitter:
London Assembly LabLibGreens decide not to earn their pay by not holding the Mayor to account. #giveBackYourSalaries
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The Gambling Commission said: "Integrity in sport is not a joke and we have opened an investigation to establish exactly what happened."
The landmark development will see all London staff working under one roof but will mean the closure of three historic studios.
Five activists were arrested after staging a three-hour demonstration which forced the closure of a tunnel at Heathrow Airport.