Reversing Britain's shock Brexit referendum would hand a "positive" and "significant" boost to the economy, the OECD said today. 

"In case Brexit gets reversed by political decision (change of majority, new referendum, etc) the positive impact on growth would be significant," the Organisation for Economic Co-operation and Development said in its latest assessment of the UK economy. 

A spokesman for British Prime Minister Theresa May stressed however that it was the government's position that there should not be a second referendum, with Brexit due to take place in March 2019. 

The Treasury also said: "We are leaving the EU and there will be no second referendum." 

The OECD meanwhile left its economic growth forecasts for Britain unchanged from its previous prediction of 1.6% in 2017 and 1% in 2018. 

Britain should seek to maintain close economic ties with the European Union to weather the impact of Brexit, added the OECD which advises industrialised nations on economic policy. 

However, the country's planned departure from the EU has worsened its existing productivity problem by increasing uncertainty and reducing business investment, it stated. 

Reviving labour productivity growth is a challenge "compounded by Brexit", the OECD said, adding that leaving the EU could reduce total factor productivity by about three percent after 10 years due to reduced trade.

The Paris-based organisation also warned that a "disorderly Brexit", one in which no trading relationship is arranged, would constitute a medium-term shock to Britain's economic growth prospects. 

"Business investment would seize up, and heightened price pressures would choke off private consumption," the organisation added in the report. 

"Negotiating the closest possible EU-UK economic relationship would limit the cost of exit," it added. 

Britain voted to leave the EU in a shock referendum in June last year. 

Ahead of British finance minister Philip Hammond's annual budget on November 22, the OECD also said the Treasury has a buffer of 1.25% of gross domestic product relative to its structural deficit target of 2% of GDP. 

It recommended investment targeted at increasing productivity, such as "spending on repair and maintenance or soft investment" if growth weakens further ahead of Brexit.