The policy is pandering to racist prejudice, rather than the actual need of the jobs market.
Will Brits do the low paid, back breaking jobs like flower and fruit picking? Not a chance. Why do you need English language skills to do either of these jobs? Jobs British people won't do, leaving crops unpicked and wasted in fields?
It will also cause a skills shortage, in healthcare and the NHS, as many junior / starting positions are beneath the £25,600 threshold.