Darktrace, a UK cyber security upstart that boasts links to GCHQ, is in talks with Silicon Valley investors to raise a war chest that would value it at $400m (£283m).

The funding round is expected to be finalised next month and would mean the company’s implied valuation has nearly quadrupled in less than a year. Negotiations are ongoing as to how much equity will be sold.

Sources close to the talks said Darktrace was seeking to top up its cash reserve in anticipation of a major downturn in technology venture capital funding.

Investors have piled money into start-ups at ambitious valuations in recent years. The herd of so-called technology unicorns – those valued at more than $1bn – is expected to face a brutal cull. A string of big names including the location app Foursquare and fitness gadget maker Jawbone have had to slash their valuations to raise cash.

Darktrace is understood to be growing rapidly despite a crowded field in cyber security, however. It makes technology that uses advanced probability algorithms to detect security threats in corporate networks.

The company, founded by former GCHQ staff and University of Cambridge maths academics, claims its approach is unique in being able to uncover previously unknown threats. Its majority shareholder is Invoke Capital, the technology investment firm set up the entrepreneur Mike Lynch after he sold his FTSE 100 software company Autonomy to Hewlett-Packard.

Mr Lynch and HP parted company acrimoniously a year after the £7.4bn deal and are now locked in a court battle over claims of sales fraud. Mr Lynch strongly denies the allegations.