Britain should be punished by its European partners if it votes to leave the EU in order to discourage other countries from leaving, former European ministers have said.

The UK was also warned many of the freedoms the UK would achieve as a result of being outside the EU would prove to be a mirage since free trade agreements, the movement of workers and the the conduct of UK financial services would still be subject to either direct or indirect EU influence.

The bleak warnings of an emasculated UK were made on Monday by former EU ministers including two former prime ministers at an event seeking to simulate the UK-EU negotiations over the terms of the UK’s continued membership. The all-day wargames session was organised by the Open Europe thinktank.

The Polish former deputy prime minister Leszek Balcerowicz said Britain would be used as example. “We should not encourage other populist forces campaigning on exit such as National Front in France or Podemos in Spain. This is a very important consideration. This is in the interests of Europe that we do not encourage other EU countries to leave. The common interest of remaining members is to deter other exits. This should have an impact on the terms Britain gets.”

Britain was also warned it would not be able to cherry-pick its best deals, and might find UK citizens inside the EU at a serious disadvantage with questionable legal status. “There is no such thing as a free lunch. Brexit is something which does not only affect your country but our country,” the former German deputy finance minister Steffen Kampeter warned. “The cherry-picking after torturing us for months is not acceptable.”

The former Italian prime minister Enrico Letta said Italy would support moving Europe’s financial centre away from London, adding that Europe could not afford such navel-gazing at a time when other parts of the world were forging ahead.

France’s former Europe minister Noëlle Lenoir said the opportunity to move the EU’s financial centre from London would be a blessing. All existing European court rulings that have protected the British banks would be obsolete, she said. Others predicted efforts would be made to woo Scotland to remain in the EU and peel away from the UK.

Ana Palacio, a former Spanish foreign minister said: “We will be [in] unchartered waters if there is a Brexit. No one is preparing for this and no one knows the future.”

The former EU trade commissioner Karel de Gucht said: “How can you expect after leaving the European economy that that economy would accept its financial centre is outside its borders?”

John Bruton, the former Irish prime minister, said: “I would regard it as an unfriendly act: a huge self-imposed, politically generated shock to our economy.”

Norman Lamont representing a post-Brexit UK at the wargame said: “The UK’s economic future would not be determined by the politicians but by the the people of this country. The EU is too remote, it is incomprehensible, we need a different sort of relationship. Trade depends on willing buyers and willing sellers, and is not determined by politics alone. I do not know what will happen and I think a constructive approach is required by everybody and acrimony should be put to one side.”