LONDON, Sept 4 (Reuters) - The stand-off between Britain and the European Union over post-Brexit trading rules for Northern Ireland threatens to create "cold mistrust" in the broader relationship between London and the bloc, Britain"s Brexit minister said on Saturday. David Frost said Prime Minister Boris Johnson"s government did not want to sweep away the so-called Northern Ireland Protocol, but did need to see "substantial and significant change". Those changes covered the movement of goods into Northern Ireland, standards for goods and governance arrangements. "I want to be clear that any response which avoids serious engagement with those ideas, and aims at just dragging out the process, will in the end not work for us," Frost said in a speech to the British-Irish Association. The EU began an infringement procedure against Britain in March over changes to the Northern Ireland trade arrangements that, according to Brussels, breached the Brexit divorce deal agreed with London last year. The bloc"s executive said in July it was holding off on the legal action after London asked for a standstill period. The protocol seeks to protect a 1998 peace accord by keeping an open border between Northern Ireland and EU member Ireland, without opening a back door to the bloc"s single market. Checks on goods between the British mainland and Northern Ireland have disrupted trade flows and angered unionists who resist any moves that they see as endangering the province"s role in the United Kingdom.