Belgium residence card - useful to migrate to UK?

No - no use whatsoever.

Unless you have a BE passport....you cant work in UK. You will still need a visa to go the UK....
With BRExit referendum coming soon...no one knows wht will happen?

Sandokan depending on where you come from in Asia you could check the UK for the entry rules. It is quite difficult there at the moment to get well paid permanent work. You would need that offer to get in there I think. My friends partner (who was African) had difficulty in getting entry to the UK after they married and he had attended University in the UK where they met and has family there. In the end they married in Africa and she stayed in the UK and he was eventually granted entry and she was working and owned her own home. Unfortunately the UK isn't so welcoming of foreign nationals as one would hope.