The prime minister has been slapped down by the UK statistics watchdog for inaccurate use of immigration figures in a podcast last week.

As FactCheck noted on Friday, Gordon Brown quoted figures from two different sets of statistics to back up his claim that net migration – the number of people coming into the country, minus the number of people leaving – is falling. He did not spell out that the figures came from different series – rather like comparing apples and oranges.

The UK Statistics Authority, which monitors the use of official statistics, told us they would look into the podcast on Friday. On Monday, shadow home secretary Chris Grayling also asked the watchdog to request that Brown “clarifies his remarks and undertakes not to mislead the public during the approaching general election campaign”.

Today Sir Michael Scholar, head of the UK Statistics Authority, wrote to the PM to say he had received representations “from several sources” about the podcast.

“I attach a note, prepared by the ONS, on these statistics,” he wrote. “You will see that the note points out that the podcast did not use comparable data series for 2007 to 2009, and that it did not take account of the revised estimate of long-term net immigration for 2007.”

“The Statistics Authority hopes that in the political debate over the coming weeks all parties will be careful in their use of statistics, to protect the integrity of official statistics,” he concluded.

This morning Brown seemed to have done his homework. He made a speech on immigration, in which he quoted from both sets of figures correctly.

UPDATE: Downing Street later accepted the original figures used were misleading.

“We accept that some of the statistics used in the Prime Minister’s podcast were not strictly comparable and as a result were unclear,” a spokesman said.

“As the chair of the Statistics Authority points out in his letter, the Prime Minister clarified the position in his speech today. The figures he used in his speech are consistent with the analysis set out in the accompanying note from Sir Michael Scholar.”