Doesn’t seem to me it would be in Labour’s best interest to call a vote of no confidence. If the government lost, Johnson could play for time for a week or two, then invite the House to dissolve parliament. If they agreed, there would be a GE, which would take place in November. Meanwhile we would have left the EU, the Brexit party would have no purpose, the Libdems would have no policies and in a more or less straight fight between Corbyn and Johnson, I suggest the Tories would walk it.