Prime Minister Gordon Brown's Labour Party has registered its worst opinion poll showing since surveys began in 1943, the Daily Telegraph reported on Friday.

It said the YouGov poll showed Labour on 23 percent against 47 percent for the Conservatives, underlining voter concerns about a slowing economy, rising fuel and food prices and a botched tax reform that have battered Brown's popularity.

Last week, Labour lost a mid-term parliamentary seat to the Conservatives for the first time since 1978, the year before Margaret Thatcher defeated Labour to sweep to office.

Coming after a drubbing in local elections earlier in May, the parliamentary by-election defeat triggered media talk about a party leadership challenge to Brown.

Brown, who took over the premiership from Tony Blair last year, does not have to hold a national election until May 2010. Under Blair, Labour came to power in 1997 and went on to win two more national elections.

The Conservatives under the leadership of David Cameron are now firm favourites to win a national election, and some Labour MPs have said their party does not stand a chance as long as Brown remains in charge.

Some of Brown's critics have given him until Labour's annual conference in September to pull the party out of the doldrums.

Brown's supporters hope the economy will ride out the turmoil created by external factors such as high oil and food prices and the global credit crunch in time for the next election.

The economy grew at its slowest pace in three years in the first quarter of 2008 and inflation is forecast to rise near to 4 percent, limiting the central bank's scope for interest rate cuts.