Chancellor George Osborne has said he wants the new regulator, the Financial Conduct Authority, to "look at the whole package" of charges for payday loans.
He said this would include considering a cap on arrangement fees and penalties as well as the interest rates, in order to put a "cap on the total cost of credit".
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Two knives were found at the scene in Islington, North London, and the suspects fled on foot before being arrested.
The violence began after a counter-protester allegedly doused a female rally organiser with pepper spray.
As temperatures climb through the day, the warmest spots are likely to be across western parts of Northern Ireland and western Scotland.