The Shadow Foreign Secretary brushed off reports that party enforcer Michael Dugher had tried to quit the election team over a "safety first" strategy.
He also denied claims he had sacked campaigning guru Arnie Graf, which is said to have further fuelled the row with Mr Dugher, insisting the American community organiser is "absolutely" going to be involved in the campaign.
The Scot told BBC One's Andrew Marr Show: "I don't think it's a great headline for the newspapers saying 'Labour team united and working for a victory' so I think we can dismiss some of the headlines.
"One of the insights of this generation of Labour leaders is that it's a totally false choice to be credible or radical. If you're not credible then people won't trust you with the governance of the country. If you're not radical people just say you're all the same. That's why I believe that we will offer credible and radical policies."
Mr Alexander also swept aside concerns about Labour's declining poll lead as he claimed the party can dominate the centre ground and win the election.
He claimed the party would soon set out more policies, saying Lord Adonis's growth commission would report "in the coming days".
An Observer poll yesterday showed Labour's lead down to just one point, with a backing of 33%, down two points from a fortnight ago.