Labor has suffered a sharp fall in popular support after a week of incendiary political claims over border protection, with the party leading the Coalition by 51 to 49 per cent in its narrowest result in more than six months.

Voters have shifted against Labor in significant numbers amid the escalating row over the refugee medical transfer law passed by Parliament last week, cutting the party’s lead over the Coalition from the previous result of 54 to 46 per cent last December.

The results, contained in an Ipsos poll conducted exclusively for The Sydney Morning Herald and The Age, are a warning sign for Opposition Leader Bill Shorten over the power of government claims of a “dismantling” of the offshore detention regime and a fresh argument that the new laws will not stop accused criminals coming to Australia.

Mr Shorten has lost some ground on his personal approval rating, with his net approval falling from minus nine to minus 12 percentage points, but the furore over borders has not made a significant difference to his standing.