George Osborne has defended his plans to offer tax-free childcare vouchers worth up to £1,200 a year to British households with annual incomes as high as £300,000, saying he wants the scheme to be simple to administer and available to those on the 40p tax rate.

Some Conservative MPs have described the scheme, announced on Monday as clumsy, while some analysts claim lower income groups may lose out depending on the number of hours they work.

The chancellor insisted the scheme was fair and that, for simplicity, it had to be aligned with existing tax brackets, rather than introducing an entirely new tax threshold. "The vast majority of people who will benefit from this are people on low and middle incomes," he said.

Defending its availability for some of the highest income groups, Osborne said the simplest way to introduce the scheme was so that it cut off at an individual income threshold of £150,000, when the 45p tax rate kicks in rather than at about £40,000, when the 40p tax rate begins. "I took the view that families earning £42,000 a year needed to get the help for tax-free childcare. I would much rather include those on middle incomes."

He added: "One of the things that I have learned in this job over the last three years is that when you are presented with complex administrative solutions they do not work in practice."

Osborne has faced separate criticism for excluding families where one parent was at home, but he insisted the scheme was primarily targeted to help families wishing to go to work but unable to do so due to childcare costs.

"This is not for stay-at-home mothers. That is their lifestyle choice. We have a proposal on married couples tax breaks which we are going to introduce in the autumn statement – that will help stay-at-home mothers." It is expected the married couples tax break will be worth around £120 a year, well below the help being offered on childcare at a cost of £1bn a year.

The childcare scheme will help some stay-at-home mothers and fathers since the tax-free vouchers will be available for parents staying at home who are in receipt of the carers allowance, and for those paid to be on parental leave to cover the costs of previously born children.

Separately, Osborne hailed the way in which the economy was growing in all sectors, saying the UK was seeing a sustainable recovery.

He ridiculed Labour's statement that average incomes had fallen by £1,300 a year since 2010, saying their economic argument had collapsed and they were physically absent from the debate. He said the UK was poorer as a result of the recession that happened under the Labour government.

Osborne denied his "help-to-buy" mortgage scheme would produce a housing bubble, saying the market was far off such a situation.

He also disclosed that the new governor of the Bank of England, Mark Carney, would produce a new policy this week on forward guidance on interest rates, a way of reassuring markets and the public that rates will not suddenly rise. The guidance was adopted by Carney in Canada where he previously worked and has been used by the Federal Reserve in the US and the European Central Bank.

Osborne also urged the UK not to turn its back on fracking as a way of exploiting recently discovered shale gas reserves. He said there was an energy revolution underway in China and the US that had dramatically cut energy costs, meaning manufacturing businesses were returning to the US. "I want to see that kind of thing in Britain. I want to see families with lower energy bills."

He said the Conservatives understood the need for a balanced energy policy. "The new regime for fracking has very clear community benefit. So we have designed a regime that is very generous for local communities where this activity might take place. It would be a real tragedy for Britain to allow this energy revolution to bypass our country . It would mean we would have much higher energy costs than other countries, it would mean jobs would go to other countries and business would leave and we would all pay a very high price for it."