Companies engaged in the controversial blacklisting of employees will be excluded from public contracts in Scotland, according to new official guidance.

Firms will have to declare if they broke relevant laws and prove they took remedial action before being allowed to bid again, the Scottish Government has decided.

Companies failing to disclose such practice may see contracts ripped up.

The Scottish Trades Union Congress welcomed the approach.

Scotland's First Minister, Alex Salmond, revealed the policy as unions hold a day of action against blacklisting across the UK, including at Westminster.

It also came as it was revealed around 1200 construction workers are to be told their names are believed to be on a blacklist, paving the way for a huge increase in legal action.

The Information Commissioner's Office is sending letters to the workers following years of campaigning by unions to seek compensation for those on the secret list.

Mr Salmond said: "We are making it absolutely clear to any company wishing to tender to supply, build or service parts of our national infrastructure, or to deliver our public goods and services, that blacklisting will not be tolerated and that they face being excluded from bidding for public contracts if found to be taking part in this unacceptable practice."

Scottish Labour MSP Neil Findlay said: "I welcome this new guidance, which is a move in the right direction on this national day of action against blacklisting, but this should complement, not replace, new procurement legislation."