Government hopes of doubling UK exports to £1 trillion by 2020 have been stymied after two years of "flat performance", according to the public spending watchdog.
Chancellor George Osborne announced the ambitious aim during last year's budget, but achieving it will be "challenging", the National Audit Office warned, as it highlighted expert forecasts suggesting that hitting the target is "not likely".
Making good on the commitment means now increasing overseas sales by 10% year on year, which will need a concerted push by the Foreign Office and the Government's trade arm, UKTI, its report said.
Although we ak global demand last year meant other European countries also saw a similar decline in export share, the UK's grip on the market has fallen from 5.1% to 3.3% since 2000.
The Government must claw back markets where it is under-performing if it is going to hit the target, the NAO warns.
Its report, Supporting UK Exporters Overseas, found that while Britain fares better than Germany, France and Italy in the Gulf, it has "not traditionally performed as well" in emerging markets such as Russia, Brazil, Turkey and China.
Forecasts from the International Monetary Fund and Office for Budget Responsibility suggest doubling exports from their 2010 level of £488 billion by 2020 is unlikely, it adds.
The FCO and UKTI have changed some of their overseas operations to help meet the target and ministerial trade visits have become increasingly high profile but must set out clearer targets for how the £1 trillion target is met.
Amyas Morse, head of the National Audit Office, said: " If the Government's ambitious objective of export-led growth is to be pursued vigorously and cost-effectively by the FCO and UKTI, the two bodies will have to make a substantial contribution.
"To do this, the FCO and UKTI need to adopt tough measurable objectives in terms of actions and results across their global networks, improve evaluation of impact, and work together more effectively."
Foreign Office minister Hugo Swire said: "The NAO report sets out what the FCO and UKTI are doing to meet the Government's ambition to double UK exports to £1 trillion by 2020, as part of our broader determination to refocus our efforts towards growth.
"We believe that the FCO has a vital role in helping British business to succeed in the global race, from supporting our exporters overseas, to pressing for open markets around the world. The report highlights steps we have already taken, from targeting more resources at priority markets, to increasing commercial training for staff.
"But there is always more we can do, and we welcome recommendations as to how we might improve our performance. We will be looking closely at these and working with UKTI to deliver the best possible contribution to British export success."
Trade minister Lord Green added: " The NAO's report highlights the key role UKTI and the FCO are playing in helping more British businesses to export and the results are coming through already. Since 2010 exports to China have increased by 91% and exports to Russia are up by 118%.
"We are working hard to achieve our ambition of doubling exports to £1 trillion and getting 100,000 more UK companies exporting by shifting the focus of our staff, working in the UK and in embassies around the world, towards targeting high-value opportunities.
"We are also providing more support and advice for UK small and medium sized businesses by establishing a global business network and opening British Business Centres in key markets across the world including India, China and UAE.
"However we want to go even further and UKTI will work with the Foreign Office to implement the report's recommendations."