IF YOU are making that final push onto the housing ladder you might be tempted to pile into a new cash version of the Lifetime Isa (LISA), which launched two weeks ago and has already attracted more than 15,000 savers.

But what if you are already squirrelling cash into the Help to Buy Isa? Modest savers could be nearly £100 worse off over two years if they make the switch into the LISA, while bigger savers may be better off waiting before taking advantage of a bigger allowance and bonus.

The LISA was unveiled last year in the final Budget given by former chancellor George Osborne. It offers up to £1,000 in taxpayer money each year to anyone under the age of 40 who is saving for a first home or retirement.

The maximum amount that can be put into the new product is £4,000 per year - £1,600 more than the £2,400 allowed in the Help to Buy version - and a 25 per cent bonus will be paid on annual contributions until the age of 50.

Consumers were supposed to have a choice between a cash and investment LISA, but until now only the latter has been available through a limited number of investing platforms. Skipton Building Society has become the first to launch a cash version, with its product paying an interest rate of 0.5 per cent.

Skipton reckons that a 25-year old who uses up the product's annual allowance of £4,000 for eight years will have a savings pot of around £40,776 by the age of 33.

According to Halifax, the average deposit required to buy a first home in Scotland is £20,729, meaning it would take just over four years for first-time buyers to accumulate that amount north of the border. Anyone going on to take out a mortgage with Skipton will also receive £250 cashback.

The first cash LISA has proved reasonably popular, despite most of the financial sector shunning LISAs more generally due to worries about mis-selling and tax complications. Mr Osborne's successor, Philip Hammond, has stood by the initiative and the Treasury is hopeful that 200,000 savers will have opened a LISA by the end of this tax year.

Rising demand will partly come from people ditching the Help to Buy Isa before it ends in November 2019, but whether you decide to move now should depend on how much you can save and how long you need to reach your target.

Those who are only saving smaller amounts (up to £200 a month) or are buying imminently may want to stay put. They would be £97 better off if they use the top Help to Buy Isa on the market from Barclays, which currently pays 2.25 per cent. Saving the maximum amount into this account both for the first year (£3,400) and the next (£2,400) will earn £131 in interest compared to £34 on the same contributions into the Skipton LISA.

Those who can stash away larger amounts for longer may want to move into the LISA before next April, as this would allow you to earn your Help To Buy bonus in May 2018 rather than having to wait for it. But you may want to delay the move until the end of this tax year so you can benefit from a higher Help to Buy rate and also hope for better cash LISA rates to emerge. Otherwise, you should stick with your Help to Buy Isa and collect your bonus of up to £3,000 when you're ready to buy.

Remember that you cannot earn a bonus on both accounts and you will forfeit it altogether -plus a further five per cent with the LISA - if you withdraw early.

Anna Bowes, director of Savings Champion, said: "You have to congratulate Skipton on the one hand for offering a cash version of the Lifetime Isa at all, but the interest rate of 0.5 per cent is incredibly disappointing. This is what happens when there is no competition in the market."

Beyond the short term, you will also have to assess whether prices will soar and ultimately squeeze the value of your LISA savings if interest rates remain inadequate. Inflation rose to 2.9 per cent in May - the highest level seen in nearly four years - and Bank of England governor Mark Carney has stated that he remains opposed to hiking the Bank of England base rate.

Investing in the stock market gives you the best chance of beating inflation and returns on cash in the long term. But you are not guaranteed to get back what you put in and markets can move both up and down – an unnerving thought if you are a first-time investor or buyer.

Steven Cameron, pensions director at Aegon, said first-time buyers nearing their goal may find the stock market “too volatile".

"Cash-based investments remove the risk of falls in value and are more likely to appeal to those saving for a house deposit,” he said. “We believe the LISA will appeal primarily to those saving for their first home as employees will almost always be better saving for retirement through a workplace pension with an employer contribution.

"It may also appeal to wealthier parents who are trying to help their children get on the housing ladder or able to pass on wealth. Even modest payments from their 18th birthday will go a long way due to the government bonus.”