UK, Ireland / Where to request Polish Birth Certificate / change of name from the UK? [15]

Merged: Obtaining Polish birth certificate in UK

I want to apply for a copy of my Polish-born father's birth certificate. I have his parent's details, the district, and USC address... Can I apply by post, or is it better to get via the Polish embassy in London? It's the piece about proving I'm a relative that makes me think the embassy route could be best.