MPs would be banned from holding second jobs under reforms of the rules governing political donations and lobbying that have been proposed by the Labour party.

Political donations from convicted tax evaders would be banned, while ministers would be prevented from becoming lobbyists for five years after leaving office under the proposals.

Legislation for the reforms would be enacted immediately upon entering office so as to prevent undue interference in a second referendum on Britain’s membership of the EU, the party said.

The proposed reforms include:

A ban on MPs holding second jobs, with exemptions for professional registrations for careers such as nurses.

Preventing political donations from “non-doms” – those who reside in the UK but claim their true home is overseas for tax purposes, exempting them paying tax on income received offshore – as well as those convicted of tax offences.

Forcing political parties to name those who attend donors’ forums such as the Conservative party’s “Leader’s Group”, which give donors contributing more than £50,000 private audiences with senior party figures.

Banning former ministers from working as lobbyists for a minimum of five years.

In a statement Jon Trickett, the shadow minister for the Cabinet Office, said: “Under the Tories, politics and government is in serious danger of becoming a playground for the rich and powerful, with decisions often made behind closed doors in the interests of a small few, at the expense of the many. This is very worrying for our democracy. The rules that are supposed to prevent this are completely ineffective. The time for their replacement is long overdue.”

The Conservative party was approached for comment.

Labour has also proposed abolishing the Lobbying Act, criticised as a “gagging law” by some for restricting charities from campaigning on policy issues in the run-up to elections, while exempting swaths of the public relations industry from registration.

The party instead proposes expanding the rules to require the registration of in-house lobbyists who work full time for a particular organisation, in addition to the specialist lobbying firms. It would also require disclosure of much more detail about the nature of lobbying work undertaken.

It also proposes expanding the register to cover thinktanks “that engage in lobbying activity”. Critics have accused thinktanks that write policy proposals but refuse to name their donors of harbouring potential conflicts of interest.

Last week the Guardian reported that it had identified 11 wealthy donors in the US who had donated almost £3m to rightwing thinktanks in the UK over the past five years. One of the recipients, the Institute of Economic Affairs, has been specifically named by Labour as an example of a thinktank that would be affected by its new policy.