Both fixed rate ISA and non-ISA products have seen the interest offered rise in April and this month is also the first time in six months that all the fixed rate averages have risen.

The data from Moneyfacts also revealed that challenger banks have driven competition and rates as they vie for the top spot in the tables.

Charlotte Nelson, finance expert at Moneyfacts, said: “However, the more mainstream banks have still yet to get in on this action, and the increases to average rates each month remain small as a result.

“ISA season has encouraged building societies to join the competition, with 10 of them launching new products into the market – not to mention many more increasing their fixed rate ISAs to offer some best buy-worthy deals.”

Nelson added that the increase in SWAP rates has also had a positive impact on the fixed rate markets. This is because it makes it more expensive for providers to fund their mortgage books, which in turn leads to an increased need for longer-term investment rates.

Further, given all the hints of a base rate rise next month, Moneyfacts said many providers are choosing to increase fixed rates to encourage savers to fix before then, keeping the interest paid out to a minimum.

“Savvy savers, however, are not being enticed by these extra increases. The latest Bank of England statistics show millions of pounds flowing out of fixed rate bonds into easy access accounts, as savers opt to wait and see if the Base Rate will rise,” Nelson said.

She added: “It’s not all doom and gloom for savers, though, as the prospect of a Base Rate rise to boost their returns brings hope. However, savers have now seen first-hand that an increase to the Bank of England Base Rate might not necessarily mean a rate rise for all. So, savers will need to keep on top of the best buys to ensure they get the best deal possible.”