British bank Barclays on Thursday said an overwhelming majority of its shareholders had approved the sale of investment management unit BGI to US fund manager Blackrock.

Barclays said 99 percent of investors had backed the disposal, according to an initial tally of votes tendered at a shareholder meeting in London. The bank will publish a final vote count later on Thursday.

Earlier, Barclays chairman Marcus Agius told shareholders the bank was in the final week of consultation about controversial changes to its pension plan for UK staff, and could review the structure to alleviate employees' concerns.

Before the meeting, staff had protested about the pension changes.

Keith Brookes, national secretary of the Unite trade union, said the bank had so far failed to address staff concerns and that the union would ballot workers soon on possible strike action.

If they remain as intransigent as they have been then strike action becomes inevitable, he told Reuters.

Barclays, the UK's second-biggest bank, agreed to sell BGI for $13.5 billion in cash and shares in June.

Barclays shares were up 5.6 percent at 355.2 pence by 1125 GMT, while the FTSE 100 share index was 1.24 percent higher.

(Reporting by Steve Slater; writing by Myles Neligan; Editing by Kate Holton)