The two leaders also lock horns over the NHS and leadership in the first TV debate of the election.
They party proposes an extra £10bn a year for schools in England, taken from a £50bn "Remain bonus".
Twitter said the stunt was misleading to the public and would not be tolerated in future - but did not take any direct action.
Brendan McGrath apologises for his "mistakes" after Ebenezer Azamati was "accosted" during a debate.
A higher rate would insulate workers from some of the risk they face, according to think tank Demos