According to the Labour Party, Mr Jefferies, 61, earns a basic salary of just below £350,000, but has share options that will be worth £1.8m when the grid is floated on the stock market.
Gordon Brown, the shadow chancellor, condemned the deal as "scandalous" and yesterday announced plans to make highly-paid executives justify their salaries at full public hearings.
He said Labour would require the electricity regulator - who has control over price levels - to question chairmen of the privatised companies on an annual basis over profits, pay and prices. Other interested parties, such as consumer groups, would be permitted to give evidence at the hearings.
Labour said the pay and perks arrangement was the largest in a long list of controversial deals for executives in the privatised utilities. Last week Cedric Brown, chief executive of British Gas, was under fire about his £1m salary and bonus package.
The Grid is owned by the 12 regional electricity companies but will be floated this summer if given the go-ahead by the Department of Trade and Industry. The company, valued at about £1bn at the time of electricity privatisation in 1989, is estimated to be worth closer to £5bn.
Present and past Grid directors have the right to buy about 570,000 shares at between £2.32 and £7.29 per each. Labour's figures value the shares at £12.50 each at flotation. Mr Jeffries was said to have 229,000 options, which if he bought and then sold immediately would net £1.8m profit. In total, the seven Grid directors stood to receive share options worth up to £6, said Labour.
A Grid spokesman said it was pure speculation to start valuing options at this stage because it was not known whether the Grid would be floated in its present form. The value will also depend on the scale of capital gains tax to be paid to the Inland Revenue at flotation and the size of a one-off rebate planned for customers. Under an employee share ownership scheme Grid shares are trading at £10 each.
However, Labour knows its campaign against "excessive" pay is striking a chord with the public and Mr Brown was stepping up his opposition."People up and down the country will find these pay and share option abuses scandalous in a company not yet publicly traded and which has a total monopoly."
Labour has already announced plans to force companies to fully disclose the pay and perks of directors, to seek shareholders' approval of pay rises and to tax share options as income rather than capital gain.