(Updates share price) LONDON, Nov 3 (Reuters) - Private-equity firm Vitruvian Partners LLP sold 11 million shares in UK cybersecurity firm Darktrace for 580 pence each, raising gross proceeds of about 63.8 million pounds ($87 million), after a post-flotation lock-up ended on Wednesday. The sale at an 8% discount to Darktrace’s closing price on Tuesday, reduces Vitruvian Partners’ stake in the London-listed company to 2.99%, according to a release from bookrunner Berenberg before the market opened. Darktrace was backed by Mike Lynch, the former Autonomy chief who is awaiting a decision on whether he can be extradited to face criminal charges in the United States, which he denies. Lynch and his wife Angela Bacares own nearly 16% of Darktrace, according to Refinitiv data. Darktrace was a standout success in a rocky year for tech listings in London, but its star has started to fade. It shares, which listed at 250 pence in April, reached a high of 1,003 pence in September. A sell-off was triggered earlier this month when broker Peel Hunt initiated coverage of the stock with a “sell” rating, saying there was a disconnect between the valuation and the revenue opportunity for the company. The shares fell to the lowest level since August in early deals on Wednesday before regaining some ground to trade down 5% at 600 pence at 1047 GMT. ($1 = 0.7337 pounds) (Reporting by Paul Sandle Editing by Alistair Smout and Mark Potter)