Not sure why that is as Angus Houston said in the press conference;
"Data from Chinese ship Haixum 01 has been analysed & discounted"
well, it sounded from first minute very odd and almost impossible that the chinese picked up a signal from +4000 meters depth with a simple cheap and small handheld locator . and its also very unprobable that the chinese patrol boat is equipped with a top secret state of the art underwater locator which outperforms the systems on hms echo or the towed locator on the ocean shield. no way.
i guess ocean shield and hms echo are the main force in underwater search, the other ships act as a support in visual search .
not sure ( because its classified ) what role the trafalgar class sub plays. little is known what real performance and what limitations its passive and active sonar has and if there is a theoretical chance it can pick up the wreck by active sonar now.
also not sure how much politics play a role. when the trafalgar class british sub searches in a known area i guess the chinese destroyer will make beyond the search also trials ans tests in locating and tracking the submarine for military reasons.
i guess the royal navy may not be amused to present the capability and limits of their nuclear powered subs.