A touch of Frost in mid-September froze out Yorkshire at Edgbaston yesterday and had the County Champions skating on even thinner ice in their bid to avoid the drop into the Second Division.

Needing at least 11 points to keep their survival hopes alive, Yorkshire were keen to make the right start by bowling out Warwickshire cheaply. But they were denied by Tony Frost, who responded to his promotion up the order by hitting his maiden Championship century.

Once Frost had gone, Dominic Ostler took over the main scoring role with an unbeaten 126, and at the close Warwickshire were 374 for five and in command of a match they should go on to win.

Both teams fielded considerably weakened teams for various reasons and Warwickshire had just as much incentive for winning as Yorkshire because they are still in with a shout of finishing second in the table and making off with £50,000 in prize money.

Steven Kirby struck an early blow before the morning mist had cleared by bowling Mark Wagh but skipper Mike Powell and Frost quickly got on top with Powell scoring freely on the legside.

Once Frost had settled in, however, he began to outscore his captain and at lunch was 63 to his partner's 57. But after adding only a single, Powell was lbw to a full-length ball from Ryan Sidebottom. The stand was worth 140 in 33 overs and Powell had struck six fours and faced 122 deliveries.

Yorkshire's 17-year-old paceman Nick Thornicroft bowled an excellent spell in the afternoon and thoroughly deserved his success when Ian Bell played a half-hearted cut to point and was caught by the swooping Gary Fellows. Frost, whose previous Championship best was 66, completed his century out of 203 for three but after making 103 off 158 balls with 15 solid boundaries he was lbw to a straight one from Anthony McGrath.

Ostler began to punish Yorkshire's tiring attack with some energetic drives as he and Dougie Brown put Warwickshire in charge with another century partnership, this one worth 112 in 32 overs.

The nearest Richard Dawson came to getting a wicket was when Brown, on 12, drove just short of the diving Sidebottom at mid-on. But Ostler continued to flex his muscles and hit a magnificent back foot square drive off Kirby to reach his century off 125 balls.

Brown was finally caught in the covers driving at Sidebottom, who appeared to have Ostler taken behind the wicket off a no-ball, the batsman's response being to straight drive the next delivery for four to move him on to 116.