In the following article the author Robert Peston says:
"I followed up by asking whether he believed in God, mentioning that the Labour leader Keir Starmer said he did not. In response Johnson paraphrased the bible, saying "the foolish man has said in his heart there is no God".
What "God" is or means is highly ambiguous. It would be more useful asking him whether he believes there is an underlying reason and meaning behind all things. Whether the Universe and our lives exist due to blind happenstance, or whether there is an intelligence underlying and coextensive with reality as a whole.