Had the exact same problem with my son a few months ago (he was just under 3). I spoke to my HV who agreed he wasn't very clear at all and asked for him to be sent to a speech therapist. They have to give you an appt within 6-8 weeks apparently, and I was worried about glue ear, deafness and other underlying issues to do with the way he was born.
Took about 40 minutes in the Speech Therapist's, she said he was 'average' for his age, not slow, but not good, just average. When I asked about the glue ear she said there were certain sounds that he was speaking (if that makes sense) and hearing that he couldn't if it was glue ear or partial deafness. All in all 40 minutes well spent, she allayed my fears very quickly and gave me one less thing to stress about! I recommend seeing your HV and asking her opinion, she sees loads of kids every week so she will be able to tell you if she thinks little 'un needs to be referred. There are sometimes reasons that kids don't speak clearly or as quickly as other's, they seemed to think the main cause with my son was that he walked very quickly (9months) and therefore had to have less communication with people as he would just get up and get what he wanted instead of asking. He also didn't go to playgroup til he was older, so had less time with other kids. I'm sure it's probably not a problem, but I know how worrying it can be, and it's definitely worth getting her checked.
Hope this helps
Schlomo :)