The Ulster Unionists have claimed that the defection of two disaffected DUP councillors to their party may not be the last.
High profile councillor Jenny Palmer and her husband John yesterday signed up to the UUP for a second time.
They quit the DUP after Mrs Palmer was threatened with party discipline over 'whistleblower' allegations against former DUP minister Nelson McCausland.
The couple described returning to the party they had left for the DUP more than 10 years ago as "going home".
Mrs Palmer yesterday revealed it was Mr Nesbitt's decision last week to withdraw the party's sole minister from the Stormont Executive that finally triggered their decision to re-join the UUP.
"I think Mike Nesbitt's announcement about walking away from the Executive was the trigger for us... and something that most people who have had so many years of it not working at Stormont would agree with," she said.
The Lisburn councillor dismissed DUP criticism of her move as "nonsense" but also added: "I don't want to get into tit for tat, this is too important a time for unionism. This is a personal decision for John and I.
"The DUP have a lot of issues to address but that is not for me now."
Welcoming the couple back into the UUP fold, Mr Nesbitt said: "They are very, very welcome back and, let me say, so are others.
"We know there are others out there who are now looking to the UUP as the way forward, because we have momentum, we have belief in ourselves and we have credibility with the electorate that we did not previously have.
"Politics is a rough and tumble game, we know that, but what Jenny, in particular, was subjected to by members of the DUP was way, way beyond the pale."
Mr and Mrs Palmer quit the DUP a few months after the Belfast Telegraph revealed the party had accused her of bringing it "into disrepute". This came after she disclosed internal party procedures and papers to an Assembly inquiry investigating claims she had made on BBC Spotlight. She had alleged a DUP adviser attempted to persuade her to change her vote on the board of the Housing Executive over contracts involving the controversial maintenance firm Red Sky.
The DUP yesterday said the Palmers had "been working with the UUP long before today".
"The timing of this announcement is further evidence that the UUP's actions in recent days are entirely about positioning the party for an election," a DUP spokesman said.