A sharp rise in deaths last year was likely to have been caused by failures in health and social care linked to funding cuts, a study has concluded.

Researchers from the London School of Hygiene & Tropical Medicine, the University of Oxford and Blackburn with Darwen council analysed data in attempt to establish why there had been 30,000 more deaths than expected in 2015, including a significant spike in January.

They ruled out errors in data, cold weather and influenza as the main causes for the high mortality rate and identified a health and care system struggling to cope with underfunding as the most likely main factor.

Last year 30,000 more people died in England and Wales than in 2014 – the largest year on year increase since the second world war.

The most common cause of deaths recorded was dementia.

Monthly deaths were higher in 2015 than 2014 in all but three months of the year, with the largest rise in January when the mortality rate was 24% higher.

The January spike constituted 10,479 more deaths than the monthly average between 2006 and 2014.

The report, published in the Journal of the Royal Society of Medicine today, said there were already “worrying signs” of an increase in mortality rates in 2016 and without urgent intervention “there must be concern that this trend will continue”.

The research found potential issues with the accuracy of data, caused for example by mass migration or census errors, were not plausible reasons for the high death rates.

Cold weather was ruled out as a major factor for the January spike in deaths as temperatures before and during the month were above average.

When considering the impact of influenza, the research found the most predominant strain circulating during the period, A(H3N2), was “not necessarily especially lethal” and there had been no significant increase in mortality during a previous outbreak in 2008-09.

The report said: “Explanations presented up until now do not conclusively explain that rise, but do provide serious cause for concern, with the deaths occurring in the context of massive disinvestment in both health and social care, and almost all NHS performance markers falling below their targets.”

Dominic Harrison, director of public health at Blackburn with Darwen BC, who worked on the research, said initial data for the start of 2017 is also showing a spike in deaths that, while not as large as 2015, was still statistically significant.

He said: “We really need properly funded government analysis of the causality of these spikes in mortality.

“It is obvious to everybody that the social care system is under significant pressure. That will inexorably rise due to a lack of capacity at a time of significant demand and the system is liable to whole system failure.

“There is a risk that if you don’t understand these spikes they will continue to happen and with greater frequency.”

A spokesman for the Department of Health produced a different set of statistics focused on the number of excess winter deaths which he said dropped from about 43,000 in 2014-15 to about 24,000 in 2015-16.

The spokesman said: “This report is a triumph of personal bias over research – for two reasons. Every year there is significant variation in reported excess deaths, and in the year following this study they fell by nearly 20,000, undermining any link between pressure on the NHS and the number of deaths. Moreover, to blame an increase in a single year on ‘cuts’ to the NHS budget is arithmetically impossible given that budget rose by almost £15bn between 2009-10 and 2014-15.”