Re: Maybe banned because there are no back-doors
The UK government actually runs something called the "Huawei Cyber Security Evaluation Centre".
They've looked through all the source code and so far have found no back-doors, only bugs.
You can even read Her Majesty's Government reports on it:
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/525761/huawei_cyber_security_evaluation_centre_oversight_board_2nd_annual_report_2016.pdf