* Carnwath says no fallout with chairman
* Says no longer able to devote enough time to role
* Says Barclays role had taken up increasing amount of time
* Carnwath had faced criticism over Diamond pay award
* One of highest-profile women in UK financial community (Adds report of ex-Barclays exec Missier payoff)
By Matt Scuffham and Tom Bill
LONDON, July 25 (Reuters) - The Barclays non-executive director responsible for former chief executive Bob Diamond's 17 million pound ($26 million) final pay package resigned on Wednesday, becoming the fourth boardroom figure to quit this month.
Alison Carnwath, who headed the bank's remuneration committee, cited personal reasons for her departure, which will increase pressure on the bank to bolster its depleted board.
Chief Executive Bob Diamond and Chief Operating Officer Jerry del Missier quit in the fallout from the Libor interest rate-rigging scandal while Chairman Marcus Agius has also agreed to leave.
"I've got a lot on my plate and Barclays takes up an increasing amount of my time," Carnwath, a 20-year veteran of investment banking, told Reuters from her home in Devon, southwest England.
Speaking to Reuters following the announcement, Carnwath said she had made the decision to quit because of the heightened demands of the role in the wake of the Libor affair.
Carnwath denied that there were any tensions between her and Agius despite reports they had clashed over the payment to Diamond of a 2.7 million pound bonus.
"Not at all. Marcus and I are on very good terms. He was a little disappointed," said Carnwath, who joined the board in August 2010.
Missier received an 8.75 million pound cash payoff from Barclays, Sky News reported on Wednesday, citing unnamed sources. Barclays was not immediately available to comment on the report, which if confirmed could spark a political outcry.
Britons are angry over a banking culture many see as irresponsible, and the government is keen for officials at banks accused of wrongdoing not to be seen to be lavishly rewarded.
"Mrs Carnwath had disagreed with the pay-off being awarded to Mr del Missier and .... she had had little choice but to resign because the remuneration committee had been able to exert little influence over it," Sky said, citing an un-named source close to Barclays.
Carnwath, 59, is one of the highest-profile women in London's financial community and has built a reputation for being a formidable, uncompromising boardroom presence.
After leaving Reading University in 1975 with a degree in Economics and German, she began her career as an accountant at Peat Marwick Mitchell, later KPMG, and later became the first female director of J Henry Schroder Wagg & Co, the investment banking division of Schroders.
Carnwath, who holds a myriad of non-executive roles, was criticized by investors earlier this year for her role on the remuneration committees at Barclays and hedge fund Man Group , where shareholders revolted over executive pay plans.
A fifth of Barclays' investors voted against her re-election after she backed Diamond's pay and almost one-third of Man Group shareholders failed to back her.
As late as Tuesday, Barclays had included Carnwath's name on a committee to which veteran lawyer Anthony Salz will report findings from a review of the bank's culture and practices following the interest rate rigging scandal.
Carnwath remains chairman of Britain's biggest real estate investment trust Land Securities and a director of Zurich Insurance Group and U.S. heavy truck maker Paccar. ($1=0.6441 British pounds) (Additional reporting by Mohammed Abbas; Editing by Erica Billingham, Mike Nesbit and M.D. Golan)