All the talk about international firm is meaningless.
In UK, they are hiring people predominantly with the UK degrees (domestic), meaning your first class from Leicester, Bristol, Leeds, etc.
In Sg, the firms generally hire people from domestic (Sg), meaning
NUS/
SMU.
If you wanted to work in UK firms in UK, you should have studied in the UK with your AAA/A or AAB/A. Not much point complaining about the state of affairs.