"This is a very important campaign," he told party workers. "We can't take anything for granted."
The Labour leader, with his eyes increasingly focused on a possible October general election, launched the party's modest but specific training plans in Tamworth, the core of the seat vacated by the death of the Tory MP Sir David Lightbown.
In a dry run for the technology which will dominate the general election, Mr Blair spoke to a news conference in London via a satellite link.
Mr Blair used a computer-aided machine tools workshop in Tamworth as a backdrop for his announcement of a pounds 150 training grant each for one million workers, provided they contribute pounds 25.
Labour has tried to fight the by-election as a government in waiting. Gavin Strang, the shadow agriculture minister, on Wednesday interrupted a photo-call on a dairy farm in the constituency to telephone Franz Fischler, the European agriculture commissioner, to demand EU assistance for stricken cattle farmers.
But the beef scare has blown apart the Tory strategy for the by-election, which was to build on party unity on Europe and continuing economic good news with their tough, ex-army candidate, Jimmy James.
At the edge-of-town Sainsbury's, it is only the hard-core who are buying beef or voting Tory. One former Tory voter said she would not be voting for Mr James. "They've known about beef for a long time and they must have known it would come out. They hoped they could fluff their way through, but I'm not buying any."
Tamworth is quintessential new Labour territory. A pleasant, prosperous Midlands town surrounded by large Birmingham commuter houses. The people are fed up with the Government and the Labour council, whose leader Brian Jenkins is the party's candidate, has achieved the highest accolade possible - no one has a bad word to say about it.
Labour's dilemma is that it won a similar West Midlands seat, Dudley West, from the Tories with a record post-war swing of 29 per cent in December 1994. Anything less than that could be portrayed as a recovery by the Tories. But even before the beef scare, a Birmingham Evening Mail poll conducted in the street had given Labour 66 per cent, 50 points ahead of the Tories on 16 with the Liberal Democratsthird on 13 per cent.
The Liberal Democrats' Jeannette Davy, meanwhile, treads the logically challenged line of admitting her chances are slim - "If we don't win here, we would like to get as many votes as possible" - and that she "would like to see a general election as soon as possible", without endorsing a Labour win as her next-best outcome.
5 Staffordshire South East 1992 general election: D Lightbown (C) 29,180; B Jenkins (Lab) 21,988; G Penlington (Lib Dem) 5,540. Conservative majority 7,192.