Attacks on the science of the BBC's Frozen Planet series by climate sceptic Nigel Lawson were "patronising", wrong and the "usual tired obfuscation and generalisation", according to a leaked internal document written by one of the show's science advisers.

The unpublished full response by Mark Brandon, a polar oceanographer at the Open University and scientific script consultant to the series presented by Sir David Attenborough, was prepared upon request by the BBC press office in reaction to an article in last week's Radio Times by Lord Lawson, in which he said that "Sir David's alarmism [about global warming] is sheer speculation".

The document was received by BBC press officers, but a spokeswoman said today that the office "had no reason to use it in the end"‚ because they were never asked to formally respond to the article by Lord Lawson, who chairs a climate sceptic thinktank called The Global Warming Policy Foundation.

The BBC spokeswoman said: "Due to the volume of press interest in Frozen Planet, the BBC press office asked one of the programme consultants at the Open University to provide general facts and figures about the science behind the programme in case there was any press follow-up to the Radio Times article. The purpose of this crib sheet was to have all the relevant information on hand to allow us to answer queries from journalists more efficiently. There was never any intention to issue this document verbatim."

The Open University has since published an edited version of Brandon's response on its website – minus any reference to Lord Lawson - under the heading: "The science behind climate change explained".

The landmark BBC One series, which attracted a series average of 8.67 million viewers, drew to a close last night with a "personal" final episode. In "On Thin Ice" , Attenborough highlighted the impact warming temperatures are having on polar regions.

Lord Lawson began his preview in last week's Radio Times: "Sir David Attenborough is one of our finest journalists and a great expert on animal life. Unfortunately, however, when it comes to global warming he seems to prefer sensation to objectivity."

He then went on to contradict the claims made by Attenborough in his own Radio Times article by stating that the polar bear population is, in fact, rising, Antarctic sea ice is expanding, and there was "no global warming at all" in the last quarter of the 20th century.

Lord Lawson's comments draw an angry response from Brandon. In his rebuttal, he said that they were the "usual tired obfuscation and generalisation".

He added that Lawson "focuses on isolated pieces of factual evidence and then delivers them in a way to imply that his isolated facts apply to the whole cryosphere [the frozen regions of the Earth]. Also particularly frustratingly he focuses on changes happening at planetary scale and implies they are relevant to the cryosphere which is what the series is about. Finally he also … confuses timescales. It is patronising in tone and in my opinion an attempt to dismiss and ridicule the programme. Fundamentally he is implying that the programme and Sir David's view is not what he calls objective. I profusely disagree."

Commenting specifically on the final episode, Brandon said: "Episode seven deals in facts and weight of evidence. It NEVER overstates the evidence or uses hyperbole and it is a brave and honest portrayal of what is going on right now. Reading those comments and re-examining the science behind the programmes confirmed this for me."

He then provides a point-by-point rebuttal to Lord Lawson's claims about the scientific evidence.

Relations between the BBC and Lord Lawson were already tense. In July, the BBC Trust published an independent review examining the impartiality of the BBC's science coverage, in which the Global Warming Policy Foundation, which is registered with the Charity Commission as an "educational charity", was described as "active in casting doubt on the truth of man-made climate change".

Separately, on Thursday, the foundation published a report written by climate sceptic and Sunday Telegraph columnist Christopher Booker entitled: "The BBC And Climate Change: A Triple Betrayal".

On Monday, the Discovery Channel, which co-produced the series, confirmed that Attenborough's final episode will be screened in the US from next March long with the rest of the series. The announcement ended speculation that the final episode would be dropped for US audiences because of its "global warming content". The only confirmed change is that the series will be narrated by Alec Baldwin in the US.