The Labour MP said the country's three biggest utility companies would receive a £100 million "bonanza" under First Minister Alex Salmond's plans to slash the main tax on business profits, former Prime Minister Gordon Brown has claimed.
He said SSE, Scottish Gas and Scottish Power - which between them recorded profits of nearly £2.8 billion last year - would share a £100 million windfall as a result of the SNP's plan to cut corporation tax by 3p if Scotland becomes independent. It would be part of an overall £300 million corporation tax cut for onshore companies.
Speaking in Ayrshire last night, he said: "The SNPs independence plans do nothing for Scots on the breadline but are a bonanza for the already rich directors in privatised utility boardrooms.
"With the Scottish Government a soft touch for the energy companies, there is an inevitability about rising inequality in an independent Scotland."
Mr Brown spoke out as a study by Durham University economist Professor Richard Harris argued that the SNP's corporation tax plan would be insufficient to close the productivity gap between Scotland and the rest of the UK.
Mr Harris said improving productivity was the most important factor for creating long term economic growth but questioned the impact of cutting corporation tax.
"Better policy options need to be considered post-2016," he concluded.
The First Minister has claimed that increases in productivity, employment and immigration would result in an independent Scotland raising an £5 billion a year in revenues by 2030.
A Scottish Government spokeswoman said: "Using the powers of independence to boost labour productivity in Scotland by just 1 per cent could increase output by approximately £2.1 billion and raise employment by over 21,000 over the long-term."