Why is Blackwater coming under such intense attack from the Iraqi government, while British and other non-US security firms are not?
There are probably several reasons, including Blackwater's very high visibility operations to keep American diplomats and others safe from attack in the Sunni Triangle.
But there's also another possible reason: Bribery. Blackwater is a stickler for following American law to the letter. Its current political problems stem from not from it having broken any laws, but because Congress failed to update the laws on hiring private security contractors even as it continued to appropriate and authorize money for the purpose.
Under the Foreign Corrupt Practices Act, it would be a crime for Blackwater to bribe Iraqi officials. And Iraqi officials are notorious for their fondness for bribes. The Ministry of Interior tried to shake down Blackwater for more than a year to pay "fees" for permits it was not required to have.
British, United Arab Emirates and other security companies in Iraq aren't accountable under the Foreign Corrupt Practices Act. Which could explain why the Iraqi leaders don't have a problem with them, even with they do the types of things that Blackwater is accused of.