The rules of order for amendments engage the constitutional principle of the financial initiative of the Crown. This precludes Parliament from seeking to impose taxes (or grant permission for public expenditure) unless requested to do so by the government. 

MPs who are not Ministers therefore cannot increase ‘a charge upon the people’, extend the objects and purposes of a charge, or relax the conditions and qualifications set out by the government when recommending a charge, as this would trespass on the constitutional preserve of the government.

MPs can seek only to reduce a tax rate or increase a tax relief, provided that the result of their amendment is not an increase in the charge (compared to the situation prior to their proposed change).

The scope for amendment is determined by the scope of the first and only amendable Ways and Means motion tabled at the start of the debate.

Historically, this motion has often taken the form of an ‘Amendment of the Law’ motion. This usually contains the statement that:

“it is expedient to amend the law with respect to the National Debt and the public revenue and to make further provision in connection with finance”.

Provisions to restrict the scope are usually also incorporated into the motion so the room for MPs to amend it is quite limited. However, this motion does enable the opposition – or indeed government backbenchers – to table amendments setting out alternative tax provisions which can, if selected, then be debated and voted on.

If the Government chooses not to table an Amendment of the Law motion, then the first Ways and Means motion generally takes the form of a motion for the charging of income tax. This usually contains the statement:

"That income tax is charged for the tax year [2021-22].

And it is declared that it is expedient in the public interest that this Resolution should have statutory effect under the provisions of the Provisional Collection of Taxes Act 1968."

For an amendment to this motion to be selected it must concern the annual charge on income tax. The scope for amendment is thus very limited.

Historically, the tabling of an Amendment of the Law motion has been the norm, except where Budgets have taken place shortly after a general election or when the dissolution of Parliament is anticipated (May 1929; February 1974; May 1997; May 2010; June 2017).

However, since 2018 the government has chosen not to table an Amendment of the Law motion for any Budget, favouring a motion for the charging of income tax, thus limiting MPs scope for amendment.

Yes, as well as limiting the scope for debate and amendment of the first Budget motion, the form of the first Budget motion to be moved – that is, whether it is an Amendment of the Law motion or not – also affects the scope for amendment of the subsequent Finance Bill.

For example, an Amendment of the Law motion, if passed, might provide scope for MPs to table amendments to the Bill in areas which may not be covered by the Budget such as tax administration, tax avoidance or tax relief. The absence of an Amendment of the Law motion limits this possibility.

Amendments to the government’s Budget proposals are rare but not unknown. For example:

• in December 1994 the House supported an amendment to freeze VAT on domestic fuel at 8%, in place of the government’s proposed increase to 17.5%;

• in March 2016 the government’s proposals were amended to provide for VAT relief on women’s sanitary products.

However, if any of the government’s proposals are amended, then a new Ways and Means motion (or motions) must be introduced to compensate for any lost revenue.

08:06 am, 14 March 2023

Hansard Society (2022), How does Parliament authorise the Government's taxation plans? A procedural guide to the Budget process, (Hansard Society: London)