I'm accepted to a PhD because the project supervisor was very impressed with a report I wrote about the subject. I'm finishing a MSc(Res) my current supervisor written me a good reference and he has also expressed interest for possible colaboration since they overlap each other's field.

However I had a poor first degree (3rd class, most people got that in my year). I wonder if there's a rule EPSRC only approve funding for students with at least 2:2 (first degree), even though my master degree would upgrade my first degree by one tier?

With good references there's no harm in applying. However the stipulation is generally that you should have a 2(i) or a 2(ii) plus a masters.

Yeah the supervisor had already said he'd like to employ me, and only waiting for the result from my final degree (the master by research), sounds like they're not too bothered about what i had in my BSc. I'm just worrying if they've known I had a 3rd they'd change their mind?