The daughter of Labour stalwart Joe Debono Grech, Joan Borg, has resigned from the party as a sign of solidarity with her father.

The letter of resignation was received by general secretary Jason Micallef last Saturday, along with that of her father, but there was no word about it after it became known that Mr Debono Grech, a prominent Labour activist for the past 50 years, had resigned.

She would not give any comments when contacted by The Times yesterday, following in the footsteps of her father who also persistently refused to comment or explain the reasons for his resignation.

She resigned as a member of the party but not as a Birkirkara local councillor. Similarly, her father did not resign as an MP or from the Labour parliamentary group - a fact which renders his status more ambiguous.

When contacted, Birkirkara mayor Michael Fenech Adami said he had only just become aware that Ms Borg had resigned from the party but confirmed that he had not received any resignation letter from her as a councillor.

When asked about her position within the council, he said: "Frankly I don't know what her status would be at the moment but I intend raising the matter formally".

There has been no explanation as to what led to the resignation of Mr Debono Grech but speculation has been rife. It varies from rumours that Mr Debono Grech is still sore about the excessive support he feels was given to Joseph Muscat by the party machinery in the 2004 MEP elections - which he also contested - to the theory that he is angry at an endorsement which the MEP, and now leader of the MLP, gave to MP Chris Cardona (who contests the same electoral district as Mr Debono Grech) in the last general election campaign.

Dr Muscat himself said on a TV show this week that he suspected the latter as being the most likely reason, as there was no indication of any problem between the two since 2004.

The writing had been on the wall, Labour sources told The Times. In fact, Mr Debono Grech, who endorsed the campaign of Marie Louise Coleiro-Preca, had been threatening throughout the race that if Dr Muscat was elected, he would resign.

True to his word, his resignation letter was received at Mile End the day after Dr Muscat was announced as the new leader of the party.

Still, the party has been trying to make Mr Debono Grech change his mind and started by holding a meeting with relatives of his on Sunday.