Assistant Chief Constable Steve Cotterill said "please do not see these two arrests as the police inquiry coming to an end" and appealed to the public for additional information.
He said: "I need additional information from the public out there to really get to the truth to what was the reason behind that fire - whilst I know the cause I do not know the reason behind it and I'm still anxious for that information to come forward."
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PM spokesman's comments come following reports that the EU is secretly drawing up plans for greater military cooperation across the EU.
The Labour politicians put their alleged differences aside to jointly highlight how remaining in the EU could help fight climate change.
Late sunshine here and there this evening - but more cloud for southern Scotland, northern England and Northern Ireland again.