In broad terms, people saving for their first home through a Help to Buy: ISA will be able to save up to £200 a month into their account. The government will then top this amount up by 25%. So, for people who manage to save the maximum each month, the government will be topping up the account with £50 for every £200 saved. The government bonus will be capped at a total of £3,000 on £12,000 of savings.

The bonus will be calculated and paid when the saver buy their first home. Accounts are limited to one per person rather than one per home so those buying together can both receive a bonus. The scheme is aimed at helping people who are saving up to buy a first home worth up to £450,000 in London or £250,000 anywhere else in the UK. Accounts can be opened for a period of four years from the start date of the scheme.

The government bonus can only be used towards a property that is being used for the first time buyer to live in as their only residence and not for a buy-to-let purchase. The bonus can be claimed at any time, subject to a minimum bonus amount of £400.

The Treasury note says the government intends the Help to Buy: ISA scheme to be available from autumn 2015. Allowing a £1,000 initial deposit means that people who are saving between Budget day and the autumn will be able to benefit from the government bonus on those savings.

The Treasury Help to Buy: ISA scheme outline is here: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/413899/Help_to_Buy_ISA_Guidance.pdf