Your mother cannot obtain an injunction through the police. The police deal with criminal matters, an injunction is a civil matter.
To apply through thecivil courts for an injunction will cost your mother about �3000.00 for the necessary two hearings but unless she has firm evidence she is unlikely to succeed.
That does not mean that you should ignore her opinion of your boyfriend - our mothers are our best friends and she no doubt has very good reason to be worried about your safety.