Alex Salmond has been rapped by a watchdog for claiming politicians in Westminster interfered to skew key economic data.

The former Scottish First Minister claimed that Chancellor George Osborne had "managed to inflate the UK growth figures" by having calculations revised to include the spending on illegal activities like drugs and prostitution.

In his final question time session at Holyrood as leader, Mr Salmond said the apparent boost was "not because the economy had improved but because the Government had instructed the officials and statisticians to change the statistics".

His comments drew an angry retort from UK Statistics Agency chairman Sir Andrew Dilnot who accused him of undermining public trust in official calculations and called for a public retraction and official correction.

In a formal letter, he told him: "I want to be quite clear that it is not the case that the Office for National Statistics (ONS) was instructed by the Chancellor of the Exchequer, or any other member of the UK Government, to revise the UK National Accounts.

"Decisions in relation to this programme of work are taken exclusively by statisticians at ONS, in line with international standards and best practice.

"The changes were part of an international agenda and were intended to ensure that the UK National Accounts continue to provide the best possible framework for analysing the UK economy and comparing it with other countries."

He said the Office for National Statistics had been entirely "open and transparent" about the changes, which were part of a Europe-wide adoption of revised standards.

"I am sure you will agree that the integrity and independence of official statistics are worthy of safeguarding," he told the politician.

"To suggest, as you did, that official statistics of national importance such as these are subject to inappropriate Government influence is potentially corrosive of public trust in official statistics.

"I would very much appreciate it if you would reconsider these comments. You may also wish to take advice on whether it is necessary to add a note of correction to the official parliamentary record."

An SNP spokesperson said: "We will reply to Sir Andrew in due course, but the point Mr Salmond was making was very clear and is not disputed by the ONS - that is, that UK growth figures have been inflated by including elements of the so-called black economy.

"And as a result of those figures, the Tory Government could hardly have been surprised to have been landed with a bill for an additional £1.7 billion - despite their anti-European posturing."