Federal Labor remains in an election-winning position but the Coalition has narrowed the gap, according to a new Ipsos poll.

The poll conducted for Nine’s Sydney Morning Herald and the Age has the opposition leading the Liberal-National Coalition 51-49 on the two-party-preferred measure, down from 54-46 in December.

Labor’s primary vote has fallen from 37% to 33% over two months, while the Coalition’s rose from 36% to 38% in the poll of 1,200 voters.

The poll also had the opposition leader, Bill Shorten, losing ground on his personal approval rating, with his net approval falling from minus nine to minus 12 percentage points.

The prime minister, Scott Morrison, saw his net approval rating bump from eight to nine percentage points, within the poll’s 2.9% margin of error.

The poll comes after Morrison last week ramped up the rhetoric on border protection following a historic loss in parliament on legislation making it easier for refugees to get medical transfers to Australia.

The bill – put forward by the independent MP Kerryn Phelps and supported by Labor – marked the first time a sitting government has lost a substantial vote on the floor of the House of Representatives since 1929.

It prompted the government to begin a significant ramp-up in its rhetoric on border policy – Morrison announced the reopening of the Christmas Island detention centre.

The home affairs minister, Peter Dutton, told a Sydney radio station the bill would allow people with “serious allegations of sexual assault or being involved in sexual relationships with young girls” to enter Australia – despite the bill containing provisions preventing asylum seekers with a substantial criminal record from entering the country.

The latest poll contradicts the broader polling trend which has shown the Coalition trailing Labor by a wider margin in the lead-up to a likely May election. Earlier in February an Essential poll carried out for the Guardian showed the opposition holding a 55% to 45% lead over the government on the two-party-preferred measure.

Meanwhile, a separate YouGov Galaxy poll of 810 Queenslanders has Labor ahead 52% to 48% in the state on a two-party-preferred basis, although 40% of those polled said they were less likely to vote for Labor because Shorten is the party’s leader.

Some 46% of respondents were against the opposition’s policy to abolish franking credits for some retirees, while 36% said the plan would have no bearing on their vote.

Despite this the Liberal National party’s primary vote dropped three percentage points to 35% since the last poll in November, against Labor which was unchanged on 34%.