The threat of industrial action in the NHS was rising last night as the Government failed to soothe mounting anger over job losses and privatisation of services.

Union bosses warned they would not stand by and watch staff suffering in a "climate of fear" while money was being "siphoned" out of the service by private companies.

Health Secretary Patricia Hewitt was left in no doubt about the scale of anger over the reforms when she addressed Unison's health workers conference in Gateshead.

She was greeted by stony silence, while delegates later booed, hissed, laughed out loud and shouted "rubbish" as she defended the Government's record.

The Minister conceded it was a "challenging time" for the NHS and for all health workers and she said there would have to be some "tough decisions" made about the future.

"We also need to be honest about what we have already achieved," she added.

Dave Prentis, general secretary of Unison, said many job losses were "inexplicable" and that the union will support members who want to take industrial action.

He said: "We will not stand by and watch staff facing privatisation and job losses suffer in this climate of fear.

"Unison will support members who feel that they have no option left other than industrial action to protect jobs and services."

Meanwhile members of the Royal College of Nursing (RCN) further increased the pressure on the Health Secretary at their annual conference in Bournemouth, conceding that industrial action was an option.

The group's general secretary said Ministers needed to "wake up and smell the coffee" and that the Government was "skating on thin ice".

The first outbreak of industrial action could hit NHS trusts that have announced job losses in recent weeks, as well as areas with plans to outsource work.

At the RCN conference, attended by more than 2,000 nurses, general secretary Dr Beverly Malone said members were considering stopping unpaid overtime - the equivalent of "work to rule".

She said the service could lose up to an extra day per week in unpaid work, but said the industrial action was a "heavy tool" and "way down the line".

"The reality gap between what the Government is saying and what we are experiencing at coal face level is very wide," she added.

Josie Irwin, head of employment relations at the RCN, added: "There's clearly a temperature out there where members are considering the possibility of action."

Thousands of jobs have been lost in recent months and many trusts face huge deficits as Government bosses get tough on financial management.

Opposition leader David Cameron hit out at the Government's "arrogant" manner in blaming the crisis on health bosses.

The Tory leader said: "Nine thousand people are threatened with redundancy in the NHS and peoples' local hospitals are threatened with closure.

"This is a crisis made in Downing Street."

He added: "You need to take bureaucracy out of the health service - the Government has added 100,000 new administrators since 1997 - and given greater independence to hospitals - that's the programme I would put in place to deal with our health service."

Labour MP Frank Dobson, a former Secretary of State for Health, accused the Govern-ment of presiding over the beginning of the break-up of the NHS.

He said York District Hospital, from which his wife was leaving after treatment, was threatened with the loss of 200 jobs. The Holborn and St Pancras MP attacked the use of the private sector to provide health services which he argued was not a cheaper option.

He said: "It is not an accident, it has been done deliberately. The chaos and damage we are seeing at present was deliberate".