The last time bankers faced angry demonstrations, some responded by pouring champagne or photocopied £50 notes from windows, but it is unlikely that protesters targeting the City next week during the G20 summit will be met by similar shows of bravado.

Many staff are being advised to dress down next Wednesday and Thursday to avoid being marked out as City workers - if they cannot avoid the protests entirely by working from home. Others have been advised to avoid leaving the office to attend meetings.

Concern about possible violence heightened when the home of former Royal Bank of Scotland chairman Sir Fred Goodwin was vandalised early yesterday morning, leaving three windows shattered and the rear window of his black Mercedes smashed. An anonymous email was sent to media organisations shortly after the attack threatening further action against "criminal" bank bosses.

The former RBS boss, who had not been at home and is at the centre of a row over the size of his pension from the taxpayer-owned bank, was said to have been "shaken" by the incident.

Many in the City believe aggressive media coverage of the financial crisis has declared a virtual open season on financial sector workers.

The financial advisory group Bluefin, which employs 500 staff in London, has set up a phone line offering staff updates next week. Staff have been told not to go to its office in Mark Lane in the City unless absolutely necessary. "As a responsible employer, the safety and wellbeing of our staff is always considered of paramount importance," a spokesman said.

A UBS spokesman said the bank would continue to assess the level of threat as it got nearer the time. "We are telling people to be cautious. If you have client meetings, do you need to have them here? Some of the banks have said dress down or try not to move around. It is all pretty obvious. "It is quite co-ordinated among the banks. We all talk to each other. I think it is different if you are in a landmark building, some are more obvious than others."

Another banker complained that we "are in an era of the demonisation of financial services".

World leaders, including Barack Obama, are due to begin arriving early next week with the summit beginning on Thursday at the ExCeL centre in London's Docklands.

The G20 Meltdown campaign is a loose alliance of organisations that will set off from four locations in London a day earlier and converge on the Bank of England, each marching behind one of the "four horsemen of the apocalypse".

A separate climate change protest group intends to set up camp outside the European Climate Exchange on Bishopsgate. Further protests are to take place outside the offices of RBS and there will be marches on ExCeL during the event.

Other action is rumoured to be planned to disrupt transport and cause chaos in the City in what many believe could be the biggest protests since the poll tax riots.

An additional 2,500 police have been drafted in at a cost of £7.5m and plan a "ring of steel" around ExCeL. Police chiefs last week called City firms to a briefing that gave advice on how to beef up security.

The protesters say they plan peaceful demonstrations. "This is not a problem about a few greedy bankers or regulators who were asleep at the wheel, it is a systemic problem," said Michael Rainsbro, who has helped organise the protests.

But even a cursory search on the internet finds more chilling threats, with one organisation, London Class War, showing Goodwin's head in a guillotine on the front of its G20 newsletter and suggesting in its manifesto: "Direct action is necessary against the individuals and institutions".

The email that followed the attack on Goodwin's house was sent from the address bankbossesarecriminals@mail.com and said: "We are angry that rich people, like him, are paying themselves a huge amount of money and living in luxury, while ordinary people are made unemployed, destitute and homeless. This is a crime. Bank bosses should be jailed. This is just the beginning."

But many appeared to be relaxed. "If you turn up for work in a bold pinstripe that might be an issue," said a Merrill Lynch spokesman, "but we have all been here before."

The banker's tale: Morale is low and the media target us

I work for a large investment bank and can tell you it's not a very pleasant environment at the moment. It hasn't been for some time: the bank has lost a lot of money over the past two years. Lots of employees have been laid off and motivation is low. The media's hex on bankers is unfortunate because the world needs good bankers.

People don't understand that most of us working for banks are not making trillions but a good salary and a decent bonus, and generally work very hard. This sort of public anger is fuelled by ignorance - as they think everybody is a top trader. It's true there were too many working in banking that didn't understand or care about the risks, but that shouldn't be held against the many diligent and highly skilled workers. I am glad the industry has shed some dead wood - it was long overdue. What I'd like to know is whether Gordon Brown will forego his pension due to his role in the credit crisis?