The only figures I have to hand are that out of those who apply for PhD funding from AHRC in the open competition the success rate tends to be 1 in 5. So a 20% chance of being successful. Some unsuccessful people will self-fund, so do the PhD anyway.
I can only offer my own experience: a shortlist of 6 for a fully funded AHRC, - although I've always wondered about the extent of the long list. I haven't asked my supervisor, - I'd love to know, but just seems like vanity to pursue it.
Not sure what purpose you intend to use it for but don't forget that people will also apply to multiple places - 8 applications for one vacancy is a meaningless figure in its own right, as you may have people drop out of the process.
Judging by this, and what I'm hearing from my own university, the numbers of applicants are much higher than the OP suggests because both overall number of applicants has rocketed thanks to the recession and there are fewer funded places. My suspicion is that numbers will be higher for projects that are already defined as it's more like a standard job application, than those where the applicant has to propose a project themselves and work with a prospective supervisor.