If you're concerned, trust your instincts. I 100% believe in this. Speak to your health visitor, or your GP. Find out if you can self refer to speech and language therapy (some LAs have a regular drop in session, which is what I mean by self-referral, and they will make an initial assessment).
When you're in the system, or on a waiting list to be in the system, you can decide whether you still need their services. Best to be on a waiting list and then come off it if your concerns are allayed, than not to be on it at all. Services are very, very stretched.
I went to a drop in SALT session when DS2 turned 2yo. I had concerns about his receptive language (understanding) and expressive language (outward expression). I had tried signing with him, which he didn't pick up at all. I realised later that he couldn't imitate, so certainly couldn't sign. At that age, he was a very happy child, very active, slept and ate well, enjoyed toys like blocks, trains etc. I had no other concerns about him.
We had some initial SALT sessions and some portage sessions. Neither had much impact at the time, but at least I felt that I was doing something. He was diagnosed with classic ASD at 3.6yo. I am glad that I followed my instincts and sought help, despite PIL telling me that DH didn't talk at that age either, and that it would come, and despite my older DS not talking very much at that age (although he had a different way of communicating his needs and observations, as he could sign).