Peugeot 307 starting problems

Hi there, I'm having a problem with my car when I start it. It's taking more and more turning over to get it started. It started to to this intermitently a couple of weeks ago and went into the garage for a few day but worked fine whilst there! Over the last few days it seems to be getting worse. As it's turning over, sometimes it sounds like the startermotor slows down then goes to normal speed again. The engine also seems to be shaking quite alot when cranking over. The car runs fine in all other aspects. The battery has also been replaced about 8 months ago. When the problem 1st started I thought it sounded like the started was slipping as it tried to start. It does not matter whether the car is hot or cold and sometimes it starts perfectly. Has anyone else had any similar problems?
Thanks.