The Government estimates about 55 per cent or 275,000 of the about 500,000 employees likely to be auto-enrolled in 2014 will either choose to stay in the scheme or neglect to opt out.
While the Government agreed with the Savings Working Group that an Australian-style compulsory savings regime was not warranted, Mr English said auto-enrolment was a form of "soft" compulsion.
"It is a bit of a shove but most New Zealanders understand the need to be careful with their spending, get their debt down and increase their savings."
National's KiwiSaver policy comes just a couple of weeks after international agencies Fitch and Standard & Poor's downgraded New Zealand's credit rating on concerns about the country's reliance on foreign savings, and a few days before Labour releases its savings policy.
But Mr English said National had been working on the plan for some time.
Labour's finance spokesman David Cunliffe said National's plan was "a timid and uncertain response to an important problem that should be a strategic priority".
"They're not committing to doing auto-enrolment, it's only a maybe if they have change to spare out of the 2014/2015 Budget and they're not going to say what the details are because they're not going to work it out until after the election."
Auto-enrolment "is really not going to go far enough". Mr Cunliffe said Labour's savings policy would be "bigger and better than National's".