Tony Blair has warned Corbyn not to fall for it.
The main point of this is: Blair has warned that Johnston's ploy is to incorporate his Brexit with the GE; that way voters are faced with a stark choice - a Corbyn government or Johnston and his cronies' government combined with their no deal Brexit. Johnston clearly thinks he would win under those circumstances.
Blair claims that the two should be kept separate. The referendum is a stand alone issue and not to be mixed up with who should run the country.
Of course, Leave zealots will use this hesitancy for their own spin....