I started working in ‘the City’ nearly 20 years ago. I have seen, especially over the past five years, some very major investment banks engage in behaviour that is certainly unethical and only legal because it exploits obvious loopholes. There are individuals I have come across with whom I wouldn’t work, and feel uncomfortable if I am in the same room.

Extremely aggressive and barely legal trading has been very profitable but was always high risk. I have argued, with the government among others, for tighter regulation of debt trading and credit ratings. Unfortunately, when markets have been performing well and investment banks have driven economic growth, being a Jeremiah has resulted in, at best, being ignored and more often being cold-shouldered. When markets collapse, it’s too late.

If ‘the City’ ever existed as a common-minded group of people, it certainly does not today. There are some greedy slimeballs, some of whom the Archbishop of York has quite reasonably called bank robbers. There are also people who are principled and generous. Many major charities benefit significantly from support from investment bankers and hedge fund managers, some of whom are unstintingly generous with both time and money.

Most of the senior bankers with whom I have dealt have been principled. However, most have also been focused on delivering targets for this year and at most the next three years. To prioritise ethical decisions this year – effectively giving up profit and pay – requires bankers to care about the very long-term future of their banks. I don’t know precisely how long most investment banking chief executives stay in their jobs, but I expect it is about three years – too short to worry about long-term prospects if shareholders will fire you for failing to live up to your competitors for one year. If investment banking is to be reformed, banks will need to change their approach from a narrow definition of compliance and risk management to one of genuine ethical scrutiny: out with the compliance officers, in with the moral philosophers. But, other than in a major downturn, an individual investment bank will find that if it loses out on more and more opportunities by taking ethical decisions, its best staff will just be poached by more successful competitors. Ethics is the best proxy for long-term decision making – but can only be imposed on all investment banks from the outside.

The Archbishop of Canterbury has criticised ‘trading of the debts of others without accountability’ and compared unfettered belief in the market with fundamentalism. The mistakes made in the past – the collapse of Enron in 2001, the dotcom boom and bust, the Russian banking crisis in 1997 – have been repeated, implausibly soon.

To avoid repeating them again, we need regulators (the FSA and the Treasury) and to be more interested in understanding markets and less interested in bureaucracy. We need politicians to be less in awe of money and less influenced by the seemingly munificent gestures of companies seeking to show they aren’t just greedy bastards (when in fact they are). Above all we need more individuals to make a stand. The Archbishops of Canterbury and York should go further and call for more Christians to work in the city. ‘I send you out as sheep in the midst of wolves; so be wise as serpents and innocent as doves.’ (Matthew 10:16).

• John Reynolds is chief executive of Reynolds Partners, an independent investment bank, and chairman of the Ethical Investment Advisory Group