Olympic building projects are at risk because skilled Polish workers are going back home and there are not enough qualified British workers to replace them, leading industry figures have said.

A fast-track training scheme is being put in place to teach Britons basic construction skills, including how to use a digger.

The Olympic Delivery Authority, the London Development Agency (LDA) and other partner organisations are having to spend £20million - 23 per cent of their training budget for London 2012 - on increasing the skills of the British workforce to meet the construction needs of the Olympics.

Iain Macdonald, head of education and training at the Electrical Contractors' Association (ECA), told The Times: “You can't rely on migrant labour. The position of the ECA is that you should have the capacity to generate the skills from the indigenous population.” Britain has become too dependent on a labour force now rapidly leaving for countries that are more prosperous, he said.

Andrew Teacher, a spokesman for the British Property Federation, said, however, that it was likely that British builders laid off in the private sector because of the economic downturn would move over to fill the skills gap in public building projects.

The ECA and LDA are funding the training of electricians who will work on building the Olympic Village, The Times has learnt. A total of 1,500 workers nationwide will become fully qualified electricians through the programme, which subsidises employer-based training. In London, where the scheme will train local residents specifically for Olympic construction projects, 140 people will benefit from a £500,000 investment by the LDA, ECA and the Government's Train to Gain programme.

Kevin Marshall, chairman of Summit Skills, the sector skills council for the construction industry, said that there was evidence that Polish builders are beginning to go back home and that migrant workers from other parts of Eastern Europe are taking their place.

However, he told The Times: “They don't seem to be as well trained or have the same work ethic as the Poles, that's what employers are telling us.

“All the way along we have been arguing that we can't rely on migrant labour. We have to put in plans for the long term.”

An LDA spokesman said that partnerships with other agencies would ensure 4,000 extra training places over the next four years. He added that despite the current economic climate an ageing workforce meant that there was a need to train more specialists in construction. He said that the schemes would not only be for the Games but also for the future of the London economy.