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Leeds Building Society has launched a new cash Isa that guarantees to increase interest paid to savers should the Bank of England base rate rise from 0.5 per cent.

Rates are tipped to rise in May but only marginally - and it won't necessarily happen. Savers with a variable rate account are also not guaranteed to feel the benefit if it does materialise.

The Leeds account currently pays a rate of 0.96 per cent, but the 12 month Limited Issue Tracker Isa promises to always pay 0.46 percentage points above the base rate.

On the up? Leeds BS's new deal promises to pay 0.46 percentage points more than the base rate

The Leeds Tracker Isa rate would therefore jump to 1.21 per cent if the base rate does rise - read our what next for interest rates round-up.

If rates go up, Britain's fifth largest building society will pass on the increase within 48 hours.

However this is still lower than the top rival one-year fixed rate cash Isa deals from Al-Rayan Bank at 1.5 per cent and Kent Reliance at 1.48 per cent.

Disappointingly few banks choose to boost savers' returns following a rate rise, according to research from Which? despite being quick to hike mortgage rates.

In the five weeks following the previous Bank of England change in November 2017, savers with nearly half of the 327 variable instant access Isa and savings accounts on the market at the time didn't see their interest increase.

Research from the consumer group showed only one in five banks passed on the full 0.25 per cent increase.

If the Bank of England raises rates twice this year, as largely predicted, this means savers could miss out on a 0.5 percentage point bump, a significant increase when savings rates are so disappointingly low.

What is Leeds Building Society offering?

The account is limited issue and likely to prove popular with savers banking on a base rate rise so you will need to act fast if you want to open an account before it is pulled. 

It can be opened online, in branch or by post with a £1,000 minimum deposit and it allows transfers in.

The account allows unlimited withdrawals without penalty.

Watch out, if you balance falls below £1,000 your interest rate drops to just 0.05 per cent. Interest is paid on maturity on June 2 2019. 

How does it compare?

There are few accounts on the market offering guarantees to track the base rate, and as mentioned above many banks won't automatically pass on increased on standard variable interest accounts.

Kent Reliance and Family BS are the only others offering a tracker Isa deals, according to research by information website Moneyfacts.

Rachel Springall, finance expert at Moneyfacts, said: 'Tracker deals are a great choice when there is a potential base rate rise on its way, as there is usually a guarantee set in place for the interest rate to pay above the current base rate.

'As an example, the Kent Reliance two year tracker Isa will always be 0.75 per cent above the Bank of England base rate throughout the two years. 

'These types of deals tend to be unique in the market, as most providers offer variable Isa's that may or may not fluctuate if base rate changes, there is no guarantee even though it is largely assumed.

'If savers are looking for an Isa that takes into account the average return of the highest rates, then the Family Building Society Market Tracker Isa could be a worthy choice. 

'It tracks the average interest rate of the 20 highest variable interest rates. 

'It's worth keeping in mind in this case, that the rate sits shy of the Best Buys, where the top Isa deals are currently 1.35 per cent from Al Rayan Bank and 1.30 per cent from Nationwide BS.' 

THIS IS MONEY'S FIVE OF THE BEST SAVINGS DEALS

The Bank of Cyprus UK pays 1.34% interest on its easy access account. The rate includes a 12-month bonus, after that interest drops to 0.85% so make sure to move your pot again to a better deal. It requires a minimum deposit of £1.

Ford Money pays 1.45% AER (1.44% monthly income) on its one-year fixed rate Isa. It is a Portfolio Isa which means savers can open more than one Isa under the same tax-free wrapper to divide cash between easy-access and fixed rates. It requires a minimum deposit of £500.

Atom Bank pays a top rate of 2.05% AER interest on its fixed-rate bond lasting one year. The minimum deposit is just £50. You must apply and manage your account via its mobile app

Gatehouse Bank pays 1.9% AER interest on one-year fixed term deposit plus This is Money readers can earn a £50 bonus for opening an account. The bank is Sharia compliant and therefore quotes expected profit rather than guaranteed interest. It requires a minimum deposit of £1,000.

RCI Bank pays 1.3% AER variable interest on its easy access deal - the best rate on the market without a temporary rate bonus. Deposits in its Freedom Savings Account have no FSCS protection, but you are covered for up to €100,000 by the French equivalent (FGDR) It requires a £100 deposit.

Check our independent best-buy savings tables