TextToSpeech setLanguage not working?

I am setting my TextToSpeech to use a particular language (English - UK), using the locale "en_GB". But it always uses my devices default language. Is there no way to set it programmatically? I have downloaded the files required for the language and when I change my TTS's default language to 'English - UK' it works but when the default is different the programmatic approach does not work. I have scoured the web to my best but am unable to resolve this issue.

    String ttsEngine = "com.google.android.tts";
    txt2Speech = new TextToSpeech(this, this, ttsEngine);
    //Locale ttsLocale = new Locale("eng", "GBR");
    txt2Speech.setLanguage(new Locale("en_GB"));

Tried several methods, but none are working. Can I not set my TTS's language programmatically?

Thank You