The big payout will fuel unrest in the industry when it is officially disclosed in BR's annual report in six weeks' time, just as 55,000 train drivers and rail workers vote on industrial action.
The performance bonus paid to Sir Bob, whose basic salary was pounds 131,000 despite moving to a three-day week during his last year as chairman, brings his remuneration for 1994/95 to more than pounds 200,000.
Jimmy Knapp, general secretary of the main rail union, RMT, said the payout was "only the tip of the iceberg" of top management bonuses in British Rail. He said: "My members are disgusted by what they know already. They will be very angry with this news. It will harden attitudes and contribute to a bigger 'yes' vote [in favour of a strike]."
BR made an operating profit of more than pounds 400m last year, which will also be announced in its annual report. BR refused yesterday to discuss Sir Bob's bonus or to confirm its size.
Sir Bob was awarded a performance bonus of pounds 48,960 last year. His bonus this year went up by more than 20 per cent, despite his move to a shorter working week. Other top BR executives received bonuses of around 22 per cent last year, and are expected to qualify for substantially increased payments in this year's accounts.
Brian Mawhinney, Secretary of State for Transport, has fixed a 40 per cent upper limit for future performance bonuses, making pounds 72,000 the ceiling for BR's new chairman, John Welsby, who is on pounds 180,000 a year.
Train drivers are being offered an extra pounds 6.45 a week, taking their basic rate to pounds 222. Average earnings, after more than nine hours' overtime, are pounds 416 a week. Station staff would see their basic rise by only pounds 4 to pounds 138 a week. BR says its "final" offer is fair and has appealed to rail workers to "think long and hard" before voting for industrial action that would be even more financially damaging for the railways than last year's strikes by signal staff.
During last week's abortive pay talks between RMT leaders and employers, Mr Knapp challenged top managers to disclose their bonuses. "They just sat and looked at me," he said yesterday. "It was like asking the Sphinx what it had for breakfast."
Henry McLeish MP, Labour's rail spokesman, said: "This is a scandal. We have been keeping a close eye on what is happening in the former public utilities. This is a worrying development."