check out the link below and read the bottom note Re: EU nationals and those not requiring a visa only need passport to be in date for period of stay....or words to that effect :-)
I was meant to be in Bansko today but got stopped at passport control in Sofia yesterday as my passport expired in Feb 09. The same thing happened to a couple in front of me aswell! Apparently you need three months on it. I was flown back to the UK and I now have to pay for a sameday passport and I fly out tomorrow! I hope the same thing doesnt happen to you! I would suggest renewing your passport if you can, I went to the office in london.