The academic at the centre of the "climategate" controversy over leaked university emails admitted yesterday that some of his correspondence had been "pretty awful".

Professor Phil Jones, the head of the of the Climatic Research Unit at the University of East Anglia (UEA), made the remark to a powerful cross-party committee of MPs, when challenged about saying he would not release data to a climate sceptic, "because all he wants to do is find something wrong with it."

Defending himself in public for the first time, Professor Jones faced a fierce grilling from the House of Commons Science and Technology Committee about the emails hacked from UEA computers, which critics say are evidence of how climate scientists continually obstruct requests for information.

The "climategate" affair has resulted in major controversy about climate change science and policy, because Professor Jones's unit is one of three centres in the world which put together the global temperature record going back to the 19th century and even earlier.

Climate sceptics say that its conclusion that the world is now warmer than at any time for 1,000 years – because of current global warming – is flawed, and have been seeking the raw data on which the record has been constructed, in order to challenge it.

The committee's inquiry is one of two being held into the affair, the other having been organised by UEA itself, under the chairmanship of the Scottish academic Sir Muir Russell.

Yesterday's evidence session had a full panoply of witnesses ranging from the noted climate sceptic and former Chancellor of the Exchequer Lord Lawson of Blaby, and Richard Thomas CBE, the former Information Commissioner who is an expert on Freedom of Information law, to three of Britain's most senior climate scientists – Professor John Beddington, the Government's Chief Scientific Adviser, Professor Julia Slingo, the Chief Scientist at the Met Office, and Professor Bob Watson, Chief Scientist at the Department of Environment, Food and Rural Affairs and a former head of the UN's Intergovernmental Panel on Climate Change.

Lord Lawson and Benny Peiser, the chairman and director respectively of the Global Warming Policy Foundation, a climate think-tank representing the sceptic camp, told the committee that the leaked emails demonstrated there was a concerted attempt to prevent the release of scientific data and also to manipulate the peer-review process.

Climategate, said Dr Peiser, had "tarnished the image of science around the world". Lord Lawson added: "The fact of the matter is that they were reluctant to provide data for a very long period".

But it was Professor Jones who held centre stage yesterday and MPs listened intently as he agreed that in the past, climate data, including lists of named weather stations, and the computer code used to analyse the data they provided, had not been made publicly available, in spite of repeated requests. He told the MPs that it was "not standard practice".

Labour MP Graham Stringer said to him: "If that's not standard practice, how can science progress?" Professor Jones replied: "Maybe it should be but it isn't."

Accompanied in his evidence by Professor Edward Acton, the UEA vice-chancellor, Professor Jones looked strained during the 40-minute session in which he was questioned at length by the committee.

Raising the email in which he wrote "why should I make data available to you when you're trying to find something wrong with it?" – which Professor Jones agreed was "pretty awful" – Mr Stringer asked Professor Jones: "But scientists make a name by proving and disproving things, don't they? The statement seems to be anti-scientific. It is an absolutely clear denial of the man's attempt to get at what you were doing. He wanted your information and you refused to give it to him? Why?"

Professor Jones replied: "Because we had invested a lot of work and resources in it, and this was before FOI [Freedom of information legislation] started." He listed other reasons for withholding data including the fact that some of the weather stations around the world which had supplied it were not willing for it to be released, but he said that the same information was available in the US.

The MPs heard that in July last year the Climate Research Unit was "deluged" with 61 Freedom of Information requests from climate sceptics, after there had only been two or three in the previous year.

Professor Action told the committee that the unit had only three full-time members. "It is a very small unit," he said. "We are not a national archive, but a research unit. The manpower involved [in responding to FOI requests] is very considerable." He said said he had not seen any evidence of flaws in the overall science of climate change – but said he was planning this week to announce the chair of yet another independent inquiry, which will look into all the science produced at CRU.

Professor Jones was also questioned on the most controversial email of all those leaked, in which he talks about "a trick" to "hide the decline". This refers to altering a graph showing that temperature recorded by tree-ring growth after 1960 no longer followed the instrumental record closely, as it once had done.

Professor Jones said the "divergence problem" was well known and had been written about in a scientific paper before the email was sent.

Leaked emails: Who is involved – and how they performed before MPs yesterday

*Professor Phil Jones

As director of the University of East Anglia's controversial Climatic Research Unit, Prof Jones has been caught in the eye of an increasingly ugly storm in recent months. At the end of last year, emails which appeared to show that the unit's scientists had manipulated climate data were hacked from the university's server and leaked online – a scandal which came to be known as "Climategate". Professor Jones has temporarily surrendered his post while two independent inquiries are conducted into the claims but has said he "absolutely" stands by the science the unit has produced, dismissing suggestions that the data was doctored to support a theory of man-made climate change as "complete rubbish".

How did he do?

Hesitant and strained, obviously under a lot of personal pressure and it showed.

*Nigel Lawson

The Rt Hon Lord Lawson of Blaby is a former chancellor who is now the chairman of the Global Warming Policy Foundation, a "think-tank" of climate sceptics. Lord Lawson is best known for the "Lawson Boom" (the period of rapid economic growth that he presided over in the 1980s), and his titantic efforts in losing weight after he left office. He has been a strong critic of the Kyoto Protocol's attempts to limit CO2 emissions and has called for the Intergovernmental Panel on Climate Change to be disbanded. He accepts that global warming may be happening, but believes that many scientists are being alarmist about its effects.

How did he do?

Bluff and expansive, as you would expect from a consummate politician, but not so good on detail.

*Dr Benny Peiser

Dr Peiser, a director of the Global Warming Policy Foundation, is a social anthropologist at Liverpool John Moores University and an outspoken "agnostic" on global warming. He has not undertaken any scientific research into climate change, but this has not stopped him from being a fierce critic of climate scientists. His own areas of research include topics such as "societal evolution and neo-catastrophism" and he endorses Lawson's view that predictions about climate change have been alarmist. Peiser is a fellow of the Royal Astronomical Society and boasts that a minor planet called 7170 Peiser is named after him.

How did he do?

Evasive and untrustworthy, did not answer some questions straight and hid behind "I'm not a scientist" line.

*Professor Julia Slingo

As the Met Office's chief scientist, Prof Slingo is responsible for making sure that the organisation adheres to high scientific standards. She admitted recently that the public were "very confused" about climate change, and that scientists had not done enough to help people understand the subject.

She has held the position since July 2008 and presided over an unsettled time for the organisation, which began with its prediction that the country was "odds-on" for a barbecue summer in 2009, followed by its suggestion last October that Britain was heading for an unusually mild winter. Climate change sceptics seized upon the errors under her leadership, using them to accuse the Met Office of allowing its obsession with global warming to influence its forecasts for the following week's weather conditions.

How did she do?

Solid and well in charge of her brief, the sort of sound scientist every politician dreams of having on their side.

*Richard Thomas

Thomas is a former information commissioner who, while in the post, raised concerns about increased video surveillance through the widespread use of CCTV cameras in public places and the introduction of ID cards. He was trained as a lawyer and has worked in citizens' advice and in posts for the National Consumer Council and the Office of Fair Trading. He was involved in the Campaign for Freedom of Information, which led to the law that many climate sceptics have used to badger scientists into providing raw data on their research.

How did he do?

A little boring and pedestrian but the kind of lawyer who would never get himself into trouble.

*Sir Muir Russell

Sir Muir is the University of Glasgow vice-chancellor in charge of the "independent" investigation into the allegations regarding the leaked emails from the University of East Anglia, which is paying for the inquiry. Sir Muir has impeccable establishment credentials as a career civil servant and chair of the Judicial Appointments Board for Scotland. However, he suffered some embarrassment when, within hours fo his announcing the membership of the inquiry team, one member, Dr Phil Campbell, editor of Nature, had to resign over previous comments on the email leak.

How did he do?

Effusive and convincing, with a touch of Scottish humour, almost breaking into song. Obviously wants to be liked.

*Professor John Beddington

Prof Beddington is the Government's Chief Scientific Adviser. He is also Professor of Applied Population Biology at Imperial College London and an expert on the economics and biology of sustainable management of renewable resources. When the scandal broke, Beddington said that scientists had to be more transparent and honest about their research. He said that it was not healthy to dismiss "proper" scepticism. "Science grows and improves in the light of criticism," he said.

How did he do?

A measured and assured performance, a man who evidently wants the science to speak for itself.