Mine bears no relation at all to what I'm doing. It didn't hold me back. What they look for is evidence of skills, overall academic ability and, above all, a highly-motivated student who is interested in the proposed topic and prepared to ride the Phd emotional rollercoaster.

I see, thats encouraging to hear. Pretty much what I was hoping someone would say to reassure me!

Having been through this myself, I'll warn you now. The PhD application season is typically Feb-April. Writing proposals is bloomin hard work and often coincides with coursework deadlines. I found the whole thing horrendous. In the knowledge that application season is coming, try to get ahead. Having written 6 short literature reviews in 6 weeks (for my 6 applications), doing 2 large bits of coursework, my dissertation and a large literature review all at the same time I can heartily recommend getting organised early!