Former Mines Minister Maxwell Mwale has resigned from the Movement for Multiparty Democracy (MMD) to join the United Party for National Development (UPND).

During a media briefing this morning at the party secretariat hosted by Dr. Canisius Banda, another defector from MMD to UPND, Mwale said the UPND was growing and deserved support from a cross section of Zambian people.

Mwale said the recent triumph in two by-elections had shown that the opposition party was growing in strength.

"I have today resigned from the MMD and joined the UPND which party's manifesto I now subscribe to and have pledged my loyalty to the party," he said.

Mwale said he would defend his Malambo seat that was nullified by the Supreme Court on the UPND ticket.

And in receiving Mwale UPND vice president Dr Banda said the party would continue strengthening its position by appealing to the general citizenry.

He said Mwale would add value to the growing structures of the party.

Mwale has previously been the subject of political pressure by the new Patriotic Front government. Throughout 2011 and 2012, Mwale has been arrested three times by the PF, who accused him of stealing bicycles which had been left over from the MMD presidential campaign, although these cases have failed to advance and are dismissed by the opposition as politically motivated.

In recent months, competition between the two opposition parties, MMD and UPND, has increased, including the fielding of simultaneous candidates in some by-elections, making it easier for the ruling party to seize the seats, some observers say.