Australia tightened their grip on the first Test at the Gabba today when they opted not to enforce the follow-on.

The home side now has a 626-run lead with two days of the match remaining, meaning England could be contemplat-ing an embarrassing losing margin of more than 500 runs.

England's batting crumbled to a dismal 157 all out in the face of some excellent bowling from Glenn McGrath, who claimed 6-50, to leave a first innings defi-cit of 445 runs.

Andrew Flintoff's men knew they would need an exceptional batting display to salvage any-thing from the Test - but few in the capacity 40,000 crowd could have predicted such a lame surrender.

Overnight batting pair Ian Bell and Kevin Pietersen success-fully frustrated Australia for 11 overs, but once their stand was broken England capitulated quickly with their last five wickets falling for 31 runs.

McGrath, one of their chief tormentors in recent years, an-swered any doubts about his ability to perform at this level at the age of 36 by claiming the 29th five-wicket haul of his Test career and his 10th against England.

He superbly exploited the cracks in the wicket to make the first breakthrough of the day when Pietersen, who had progressed to 16 after over an hour at the crease, shouldered arms and was deceived when the ball nipped back and hit him on the pads.

Television replays were incon-clusive about whether the ball had hit Pietersen in line, but umpire Billy Bowden had no hesitation in ending his defiant innings.

Five balls later England plunged into further trouble with captain Flintoff pushing forward defensively and edging a Brett Lee outswinger behind to wicketkeeper Adam Gil-christ.

It was the start of England's demise and but for Bell's deter-mined 50 - which spanned nearly four hours - they may have slipped to an even lower total.

Bell, who averaged just 17 in the 2005 series, found a willing ally in Geraint Jones and they ensured England suffered no further setbacks for 21 overs during a determined 47-run stand.

But just four overs after lunch, however, Jones was trapped leg before by a full-length McGrath delivery which nipped back and hit back in his crease.

McGrath almost claimed his fifth wicket of the innings three balls later with new batsman Ashley Giles fending off a short delivery. Ponting took a diving catch at second slip only for the ball to escape when he landed.

It took a change of bowling for Australia to finally end Bell's resistance with Stuart Clark introduced as a replacement for Lee - with his second delivery he tempted Bell into edging to Ponting at second slip.

Clark quickly removed Mat-thew Hoggard to a catch behind two overs later and Steve Har-mison continued an unhappy Test by earning McGrath his fifth wicket by also edging be-hind.

England's miserable demise was completed when Giles top-edged an attempted slog off McGrath and Matthew Hayden ran back from gully to take the catch.

Just to underline their domi-nance, Justin Langer finished the day unbeaten on 89 while Ponting had reached 51, the pair sharing an unbroken 113-run partnership.