A new poll shows that Corbyn has a 13 point lead over Osborne, while has closed the gap with Cameron from 24 points to seven points.
Mayor of London Boris Johnson has a five point lead against Corbyn, according to the poll by YouGov.
Meanwhile, the UK's chances of staying in the EU now appear to turn on Corbyn, with the YouGov poll finding that Corbyn is the most trusted politician when it comes to the EU.
Trust in Corbyn has increased, while trust in Johnson, who follows, and Cameron has fallen.
The Labour leader today gave a speech on the EU (but also talked about steel and tax transparency), where he outlined his support for Remain from a socialist stance, pointing to workers' rights, the environment and tackling international tax avoidance.
Last week the Prime Minister - as well as Corbyn, Osborne, Johnson, Nicola Sturgeon and others - posted their tax returns in the wake of the Panama papers.
However, YouGov states that Cameron's slip in approval is largely related to the EU referendum, and not due to his tax affairs.
Voting intention on the EU is evenly split at 39 per cent a piece, ahead of the referendum on June 23.
The previous YouGov poll, which was carried out a week ago, put Remain on 40 per cent and Leave on 38 per cent.
Polling has been increasingly tight recently, indicating that the outcome of the referendum will depend on which side can better motivate its supporters to turn out and vote on the day.
Meanwhile, voters oppose the government's decision to send out a pro-EU leaflet, costing the taxpayer £9m. Some 49 per cent say it was wrong, and 29 per cent back the move.