Since we are on a public stock exchange he can't publicly state that he in the future intends to buy any shares, because that would illegally manipulate the price. (Price going up because they are expecting Ratcliffe to buy them.) He would risk fines and maybe more.
What's most likely is there's probably a gentleman's agreement that within a set time Ratcliffe will make the Glazers an offer for their remaining shares (or at least majority), with final price depending on certain factors, likely because they couldn't agree on future valuation at the time INEOS became minority owners. (Glazers thinking it will be worth more because of some reasons, and Ratcliffe thinking it should be lower than that and would prove it over time.)
And at the same time this happens we might also see an offer to buy the Class A shares on the stock exchange, but then that price is set at that specific time, and won't fluctuate from speculation because Ratcliffe at some point told the media that he will buy everything.
If they still can't agree on the final price then the Glazers don't have to sell to Ratcliffe, and they are protected by including the right to sell with drag along (forcing Ratcliffe to sell his shares) to others after 18 months if they want to sell their shares but Ratcliffe doesn't bid as high as others would.
But it wouldn't have made any sense for either party to enter into such an agreement if they didn't both believe a future full/majority sale would happen.