MEPs leaving Brussels after next month's election will receive a payoff of up to £157,000, in addition to other perks, as part of a "golden goodbye".

Details of the package, circulated to MEPs in a document that was handed to the Observer, have further ignited rows about the benefits awarded to politicians in the European parliament.

All MEPs who step down or lose their seats are entitled to a "transitional allowance" of at least £39,000. The value of the payment increases with length of time in post, meaning the longest-serving MEPs could receive two years' salary after leaving. The allowance provides one month's salary for each year an MEP has been in parliament, with a minimum of six months and a maximum of 24.

The revelation follows a row last week over the second pensions to which many members of the European parliament are entitled, in addition to their statutory pension. The longest-serving MEPs accrue statutory pensions of up to £55,000 – 70% of their salary. They are entitled to draw this non-contributory pension, which is funded solely by the taxpayer, at age 63.

Many MEPs also have a second European parliament pension scheme, which is expected to pay out up to £41,000 a year. The fund, which closed to new applicants in 2009 and stopped accepting contributions, was criticised last week by Tory MP Philip Davies as "the perfect example of the grotesque self-serving extravagance of the EU".

Public anger escalated last week after it emerged that an "actuarial deficit" in the second pension scheme will require an extra £187m of taxpayer funding to plug the gap. UK taxpayers have already contributed more than £100m to the fund.

Out of Britain's 73 serving MEPs, 38 contributed to the European Parliament's "additional voluntary pension scheme". According to documents leaked to Hans–Martin Tillack, a German investigative journalist, and think tank Open Europe, many high-profile MEPs are members of the scheme, including Syed Kamall, Leader of Conservative MEPs; Glenis Willmott, the leader of the European Parliamentary Labour Party; Sir Graham Watson, the president of the EU–wide Alliance of Liberals and Democrats for Europe; and Nigel Farage, leader of Ukip.

Departing MEPs receiving the transitional allowance or drawing their pension are entitled to reimbursement of two-thirds of all their private medical expenses, and those of their spouse or long-term partner, and children up to the age of 21.

In addition, MEPs leaving the European Parliament at the end of June are also entitled to half of their general expenditure budget for the next three months after their depa ture: a lump sum of £5,300.

The European Parliament budget also covers the relocation of the contents of each departing MEP's Brussels office, paying for up to 15 special removal boxes to be delivered back to the member's home country.

Jonathan Isaby, chief executive of the TaxPayers' Alliance, heaped criticism on the package. He said: "British taxpayers will be staggered at the level of these golden goodbyes. MEPs who either voluntarily step down or are deselected are in no way comparable to somebody being made redundant, because they are affectively on a five-year fixed term contract, subject to renewal by the the electorate.

This is yet another example of public sector largesse which is completely unnecessary and unaffordable. The system urgently needs to be reformed."

Nikki Sinclaire, West Midlands MEP for the We Demand a Referendum Now party, added: "The point needs to be made that this generous deal, and the high remuneration of officials and politicians generally, is the cost of EU membership. This is just another example of why we the British people should determine whether this level of expenditure is worth it."