Many people who live in the area where the potash mine could be built say that they are worried that, if built, it could spoil one of England's most beautiful areas.
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Boris Johnson is on Teesside at Conyers School in Yarm. Our Political Editor Paul Brand is there
A study by the University of Oxford forecasts an increase of more than half a million foreign-born people in England between 2011 and 2014.
Paul Brand is joined by four new Parliamentary candidates for a lively debate on the economy and immigration. Watch the programme here: