By Ilaria Grasso Macola Transport for London (TfL) has called on the union RMT to cancel the Tube strike on 19 August as walking out will only increase the public body’s financial risks. “I need to be really clear with you, that taking further industrial action at this time will do nothing but undermine our negotiations with government and simply increase the challenge that we need to meet,” TfL’s director of people and cultural change Fiona Brunskill said in a letter to RMT’s general secretary Mick Lynch. “I need not spell out the dire consequences for TfL and London Underground if we are una…