Cars were set alight and masked people pelted a police van with petrol bombs on Saturday on the second successive evening of disorder in pro-British parts of Northern Ireland amid rising post-Brexit tensions in the region. Many pro-British unionists fiercely oppose the new trade barriers introduced between Northern Ireland and the rest of the United Kingdom as part of Britain’s departure from the EU and have warned that their unease could lead to violence. Political leaders, including Britain’s Northern Ireland minister, had appealed for calm earlier on Saturday but police said they were attending reports of disorder in Newtownabbey on the northern outskirts of Belfast. A video posted on Twitter by the Police Federation for Northern Ireland showed four masked individuals flinging petrol bombs from close range at an armoured police van, which they also kicked and punched. Fifteen officers were injured in the Sandy Row area of Belfast on …