The Treasury must "stop meddling" with the body which aims to help UK companies compete in a global market, according to MPs.
The Commons trade and industry committee commended UK Trade and Investment (UKTI) for its "successful record" in promoting foreign investment in Britain.
But Wednesday's report raised concerns that UKTI's five-year strategy - which focused on improving UK marketing - would only be successfully implemented if the government stopped "adjusting the priorities and structure of the organisation".
The report noted that the four-year-old UKTI had already undergone three separate strategy renewals and warned that Gordon Brown taking over at Number 10 may "lead to further damaging upheaval for UKTI".
"UKTI does a valuable and commendable job, especially given that it has been struggling with multiple changes in strategy imposed from on high," said committee chairman Peter Luff.
"It must be left to get on with this job."
The committee also raised concerns over the role of English Regional Development Agencies (RDAs) abroad.
RDAs - created as part of government attempts to increase prosperity in England's regions - receive some £15m funding from UKTI every year.
But the report warned that overseas RDA offices in the US, Australia and Japan were competing against each other and wasting money.
Luff called on the government to "address urgently" the role of the RDAs.
"There is confusion about who is actually responsible for trade promotion, and an extraordinary situation when it comes to offices abroad, which are competing with each other, confusing investors and wasting taxpayers' money," he said.
