Key Points:

The Government's budget has not helped its election odds with National firming as the favourite to win the election, according to Australian bookmaker Centrebet.

National was paying $1.47 when betting opened in February this year, but that had since firmed to $1.42 with one Auckland punter putting $5000 on the party in recent days.

By contrast Labour's odds had lengthened from $2.60 to $2.75.

The election is expected in late October or early November.