Plans to allow the re-selling of existing annuity contracts were outlined at the weekend, following much speculation.
Chancellor George Osborne is expected to rubber stamp the proposal in the Budget and flesh it out further when he addresses the House of Commons at 12.30pm.
He said: "There are 5 million pensioners who are locked into annuities they have already bought. They should have the same freedoms as we have given everyone else.
"For most people, sticking with that annuity is the right thing to do. But there will be some who would welcome being able to draw on that money as they choose - the same freedom we are offering those approaching retirement in April this year.

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"So I am going to change the law to let that happen and make sure we have the right guidance in place. People who've worked hard and saved hard all their lives should be trusted with their own pension.
"Currently people wanting to sell their annuity income to a willing buyer face a 55% tax charge, or up to 70% in some cases. The government will remove this charge, so people are taxed only at their marginal rate."
It has been widely reported this morning that Mr Osborne is likely to axe the annual paper tax return, with a move to automatic digital recording.
Users would be able see all the taxes they need to pay under these plans without having to complete an annual tax return. The idea is that they will have the ability to pay taxes they owe when it suits them and pay in instalments or by direct debit by linking their tax return to their bank accounts.
Various national media have reported that they also expect Mr Osborne to slash the lifetime pension allowance from £1.25m to £1m.
A further increase in the personal income tax allowance is also predicted.