More than 60 Brexit-supporting Tory MPs have written to Theresa May to insist the UK make a clean break with the EU.
The MPs say the UK must not be stopped from negotiating trade deals with other countries, once it leaves the EU, and must gain full “regulatory autonomy”.
The letter was sent by the European Research Group of Tory backbenchers, headed by Jacob Rees-Mogg.
In other Brexit news, a group of pro-Leave economists claim to have “comprehensively debunked” leaked government forecasts predicting a hit to the UK economy outside the EU.
The Whitehall forecasts – which predicted lower growth across the UK as a result of Brexit – sparked a row when they emerged last month.
Now Economists for Free Trade have published their “alternative” calculations, saying the civil servants’ version ignored what they said were the “clear objectives” set out by Mrs May of free trade with Europe and the rest of the world.
Using government models, this would suggest a 2% rise in GDP over 15 years, the group claimed.
Mr Duncan Smith said the report “deserves to be taken very seriously”.
To read the BBC’s report in full, click here.