The Conservatives must not "become complacent" in the run-up to the next election just because of improved opinion polls, David Davis has said.
Mr Davis said Mr Brown had brought his troubles on himself
The shadow home secretary told BBC One's Andrew Marr show that the Tories would still have to "battle" against Gordon Brown's Labour Party.
But the British people were "listening to us" again, he added.
The comments come as one opinion poll suggests the Tories have a seven-point lead over Labour.
This follows Mr Brown's decision not to call an autumn general election and the announcement of Conservative plans to raise the inheritance tax threshold to £1m.
The prime minister has also been bedevilled by a row over troop withdrawals from Iraq and allegations that the government had "stolen" Tory ideas by pledging to raise the inheritance tax threshold for couples to £700,000.
Mr Davis said: "Ten years as chancellor and now to copy the shadow chancellor's policy - what sort of a vision is that?"
He said of Mr Brown's downturn in the opinion polls: "Frankly, it was more Gordon Brown than us who did it."
The prime minister had "fractured this carefully cultured image" that he was not a "man of spin".
Mr Davis said: "The raw truth is we've been behind in the polls over the summer in Brown's honeymoon."
He added that, behind the scenes, a "transformation has been going on in British politics. People are listening to us again."
Mr Davis denied criticism that the Tories were creating policy in hurry.
He said: "The things we have been putting out on public display in the last few weeks - because we thought there was going to be an election called this week - are things we've been thinking about for some time."
Of the period since the Conservative Party conference earlier this month, Mr Davis said: "The party rose to the occasion and has had the best couple of weeks since 1992 [when it last won a general election]."
But he warned: "We are going to have to battle with them [Labour]. We cannot forget that and become complacent over the next 18 months."
Mr Brown has said he considered calling an election but his "first instinct" was to set aside more time to set out his vision.
This, he added, showed "real strength and real decisiveness" and would allow him to make the correct long-term decisions about the UK's economy and the security.
An Independent Communications and Marketing (ICM) opinion poll for The Sunday Telegraph puts the Tories on 43%, Labour on 36% and the Liberal Democrats on 14%.
The poll's findings were obtained from a random sample of 1,010 adults phoned on 10 and 11 October.