It should be ok.
My wife has German / UK dual nationality. She doesn't have a UK passport. She's never had any issues getting back into the UK on her German one. However, she has been asked if she has residency a couple of times (once by Dutch border police last year, once by UK border people this year). Each time, saying that she had UK nationality was enough and was not challenged.
We agreed that, if she looked different (black, young / male, Roma, etc, etc) things might not have been so easy, and it probably was time to get a UK passport to save future hassle.
My daughter has dual nationality and had only a German passport to begin with but I got her a UK one earlier this year to avoid any such issues.