Unless they're actually a long way down the road to making you bankrupt already i.e. the petition is to be heard before the IVA creditors' meeting, then he's talking b*******s.
Once the meeting has been held, assuming the IVA is approved, then creditors are prevented from taking any further action, so, given the length of time that it would take for them to make you bankrupt starting from scratch, they've got no way of doing this before your creditors' meeting.
Of course, if the meeting does not approve the IVA, then you're back to square one again and yes, the creditors could take bankruptcy action.
IVA proposals can be protected by an Interim Order of the Court up until the date of the creditors' meeting. The interim order would prevent creditors from taking ANY enforcement action for a limited period. Until the Insolvency Act 2000 this used to happen in every IVA, now it is no longer a requirement and in the great majority of IVAs they are no longer applied for.