Broad says keeping Clarke quiet has been key so far

LONDON (Reuters) - England will continue targeting Australia's under-pressure skipper Michael Clarke as they try to secure an Ashes series victory at Trent Bridge this week, according to fast bowler Stuart Broad. Clarke, like most of the visiting batsmen, has struggled in the English conditions and is averaging 18 compared to his test career average of almost 50. He managed only 13 runs in two innings at Edgbaston last week as England won by eight wickets to move 2-1 ahead. "We obviously do a lot of research on him because he averages something like 52 in over 110 tests which is remarkable, the career he's had," Broad, England's leading wicket taker in the series with 12, told a news conference. "We talk a lot about him and we're proud of the way we've bowled at him so far. "We've made it hard for Michael. We know how dangerous he is. He is such a key player for them and it's been going well so far." Momentum is with England but this unpredictable series could easily take another swing on Thursday at Trent Bridge where Broad says England will have to be "right on the money" against a wounded Australia team. "It's about making sure our game plan is dead right and not to worry too much about what the Aussies are doing," he said. "We know they are a dangerous team. None of the tests have been very close have they? Not like 2005 where each game went to the wire. It's been a fascinating series." Australia's pace bowler Mitchell Johnson describes the fourth test as a "grand final". "There is no avoiding it -- we were very disappointed with our performance in Edgbaston. We just didn't bat well and we didn't start very well with the ball either," Johnson, who reached the 300 test wickets landmark at Edgbaston, told Sky Sports. "What's going on out on the field has a very immediate effect on how everyone else is feeling back in the dressing room. The mood can change a lot during the course of an innings. "We've just got to focus on what we've been doing when we've been playing well. We have to take it one day at a time, one innings at a time and try and build those partnerships like we did at Lords." (Reporting by Martyn Herman, editing by Pritha Sarkar)