Newborn baby deaths appear to be rising among the poorest groups in England, according to information given to the independent MP Frank Field, who is calling on the government to investigate.

Infant mortality had been stable or dropping for eight of the 10 years from 2007. But in 2015 and 2016, the trend appears to be starting to go the other way. In 2015 there was an increase in the newborn baby death rate for the two groups with the lowest incomes and, in 2016, infant mortality went up in four out of five income groups – all but the most affluent.

While two years of data cannot establish a trend, Field fears it is a signal and has asked the government to investigate.

“I have asked the government to set up an inquiry to try to explain what the forces are at work that give rise to those figures,” said Field.

He is concerned that rising infant mortality may be linked to increasing poverty caused by austerity and changes to benefits. “2015 started the cuts in benefits and goodness knows what else,” he said. “So prior to that we had caps and limitations on rises to 1% and so on. Then we got into the serious business from 2015 onwards of actually cutting benefits in money and certainly real terms.

“Often mortality data are the canary down the mineshaft,” he said. “Those that are fragile are most vulnerable to harshening conditions.”

Field’s data comes from the UK Statistics Authority, which was asked by the Cabinet Office to respond to his written parliamentary question about the annual infant mortality rates in England by household income quintile for each of the past 10 years. The data was collected by the Office for National Statistics.

It shows that the infant mortality rate has declined markedly since 2007, when it was 6.2 in the lowest income group. By 2014, that was 4.8 per 1,000 (860 deaths). But in 2015, the rate rose to 4.9 (874 deaths) and in 2016, it was 5.1 per 1,000 (913 deaths). A similar pattern is seen in the next to lowest income group, from 3.5 to 3.8 to 4 per 1,000 (612 deaths).

Field said he is “trying to get as much data as possible to find out what’s going on with the poorest and what action can be taken”. He also wants to know whether the ONS should be collecting data that it does not at the moment. As a result of Field’s Feeding Britain campaign, the ONS is looking to see what meaningful data can be collected on hunger.

Prof Sir Michael Marmot, director of the UCL Institute of Health Equity in London, and the author of a seminal 2010 study called “Fair Society, Healthy Lives”, said inequalities are increasing. “The first thing to say about the data is that it is only a couple of years and one would not want to build a strong case of worsening inequalities on so few data points.

“That said, inequalities are increasing. Infant mortality is low in all groups – a welcome trend – but the trends are in opposite directions: going down in the higher socioeconomic groups, going up in the lower.”

In a recent Lancet commentary, Marmot pointed to housing costs as well as changes in taxes and benefits as causes of poverty. The Institute of Fiscal Studies “showed that the chancellor’s 2015 budget was regressive: for families with children, the lower the income the more they would lose by 2019 from changes to tax and benefits. Universal Credit will add short-term hardship,” said Marmot, whose 10-year update of the 2010 review will be published in February.