HIGH-TECH industries suffered a double whammy last night in a turbulent day which saw billions wiped from the value of electronics and telecoms companies.

First, British firm Marconi saw more than £3.6bn slashed off its market value after trading resumed in its shares following a gloomy profits warning.

The company's share price plummeted more than 50 per cent as investors sold up in droves.

Secondly, thousands of workers at Hewlett Packard were asked to accept a ten per cent pay-cut in return for an extra eight days' holiday.

Staff across the country were told they had "to rally behind" the company, which has been hit by the global slowdown.

Hewlett Packard hopes to save as much as £100m from the cost-cutting drive. It employs 3,700 staff in the UK and about 90,000 worldwide.

Marconi said it had been hit by weaker sales as it cut 4,000 jobs from its worldwide workforce.

In the UK, Marconi is closing its factory at Poole in Dorset.

The company employs about 500 staff at the site on the south coast and the closure is expected to be the first phase of up to 1,500 job cuts in the UK.

Union bosses are due to meet Marconi management onTuesday to discuss the fate of the 500 workers in Poole.

Danny Carrigan, national officer of the Amalgamated Engineering and Electrical Union, said he wanted to avoid compulsory redundancies.

''We are obviously very disappointed that Marconi has found it necessary to look at a plant closure. The UK needs a strong Marconi,'' he said.

''Our priority is to safeguard the future of the workforce, to avoid compulsory redundancies and to explore the options of relocation, redeployment and retraining."

Marconi's share plunge dragged other tech and telecom stocks down in its wake.

The news will increase the pressure on North-East tech companies such as Filtronic, in Newton Aycliffe.

The West Yorkshire group has been seeking a financial white knight to help it run the former Fujitsu microchip plant purchased nearly two years ago. Losses at the Aycliffe factory are running at £1m a month.

Filtronic hoped the factory would supply chips for next generation mobile phones but the collapse in the telecoms industry has thrown those plans into doubt.

Now Filtronic is in discussions with a leading aerospace and defence equipment manufacturer to form a joint venture to run the plant.

David Page, economist at City stockbroker Investec, said small investors with high-risk tech-based ISAs would be hit by the fall.

But he said the impact on pension funds that invest part of their cash in Marconi would be relatively small.

''The company is just one stock. It has gone down 50 per cent, but the effect on the FTSE as a whole is much smaller.

He added: ''Pension funds invest over time so it is not that relevant where the daily price is.''