Campaigners dressed in doctors' coats and armed with fake blood are planning to close 30 high street banks on Saturday in the biggest direct action to date against proposed changes to the NHS.

More than 30 groups across the country are expected to occupy major high street banks, turning them into mock hospitals and setting up "operating theatres" inside to draw attention to the banks' role in creating the deficit.

Dubbed "the emergency operation", the national action has been organised by the anti-austerity campaigning group UK Uncut, which has staged a series of campaigns against tax avoidance and public spending reductions since it was formed in October.

Health worker and UK Uncut supporter Rosie Beech, 29, who will be joining the protest, said: "David Cameron said he wasn't going to cut the NHS. He lied. 50,000 NHS staff will lose their jobs, whilst the taxpayer continues to subsidise the banks. Why is the government cutting the NHS and privatising what's left rather than forcing our broken banking system to pay up?"

In a sign of increasing unity between trade unions and direct action groups, the Public and Commercial Services union (PCS) is encouraging members to attend UK Uncut actions.

The protest comes three days after two activists – one from UK Uncut and another from the health campaigning group NHS Direct Action – were arrested after they entered the health thinktank 2020health to protest against the organisation's role in the health reforms.

The two accused the Metropolitan police of "political policing" and were released without charge after six hours.

Saturdaywill see UK Uncut's first big action since the arrests of 145 protesters during a sit-in at Fortnum & Mason on 26 March, when more than 250,000 people took to the streets to protest against government spending cuts.

UK Uncut activist Josephine Hill, 34, who was arrested for taking part in the occupation, said: "I will not be intimidated out of protesting by blatant political policing. It is vital that we continue to take action against the government's brutal cuts agenda, especially the wholesale destruction of the NHS."

The latest action is also supported by the anti-poverty charity War on Want and comes as research commissioned by PCS and carried out by the Tax Justice Network shows that the UK is losing £18bn a year through tax havens.

Dave Tucker, senior campaigns officer at War on Want, said: "Cuts would not be necessary if rich companies and individuals paid the tax they owe. The government has made little progress on its promises to close tax havens. This report follows UK Uncut's exposure of tax dodgers and identifies many options for ministers to chase the missing billions."

PCS said it was calling on members to support the action and added that the two groups were working closely on a range of campaigns. "UK Uncut activists have attended many PCS protests and events, and have willingly shared with us their innovative approach to campaigning and communications, particularly their use of social media," a spokesman said. "We are now working together on more specific campaigning ideas and look forward to continuing to press for tax justice and for proper resourcing of public services."

• This article was amended on 28 May 2011 to correct the name of the thinktank 2020health