Competition between hospitals does not necessarily improve quality, new research has found.
Experts said more research is needed before conclusions can be drawn about the effect of recent reforms on hospital quality and merits of the Government's proposals to extend competition.
Professor Gwyn Bevan and research student Matthew Skellern, from the London School of Economics and Political Science, say the jury is still out on the effects of hospital competition on quality of care in the NHS.
Their views, published in the British Medical Journal online, come ahead of the second reading of the controversial Health and Social Care Bill. The Government has argued the reforms, which include a push for more competition, will improve patient care as well as helping make £20 billion of savings.
Prof Bevan said the plans come after two eras of hospital competition - the "internal market" in the 1990s, and a second introduced by New Labour in the 2000s. He said studies of the second era suggested greater competition led to lower hospital mortality, contradicting previous findings that competition in the NHS was largely ineffective or had negative consequences.
Other studies looking at the effects of introducing patient choice in elective surgery assumed competition would improve elective surgery, requiring hospital management to improve quality, the researchers found.
But arguing in the article, published on bmj.com, they say: "It is equally plausible, however, that such competition for elective surgery might, through diversion of management effort, negatively affect the quality of other hospital services."
They added: "A key finding of these two studies is that introducing patient choice for elective surgery in the New Labour market did not reduce quality elsewhere in hospitals.
"We believe there are strong grounds for introducing patient choice into the NHS as an end in itself, given its potential to empower patients and give them greater control over the conditions of their care."
The experts question the use of hospital mortality rates to judge the impact of competition on the quality of elective surgery, because deaths after elective surgery are so rare that another measure is needed to assess quality. They say how patient choice has affected outcomes in elective surgery remains an "open question", concluding more research is needed.