Santander debit and credit card users can earn up to 15% cashback on spending from today, but customers will have to activate each cashback deal before they spend.

With bonuses of up to £125 currently on offer if you switch current account, banks are pulling out all the stops to keep hold of their existing customer base (see our Best Bank Accounts guide for the top deals if you're thinking of switching).

Santander is already popular with current account customers thanks to the market-leading 3% interest it pays on balances of between £3,000 and £20,000, with recent figures showing it was second only to Halifax (which offers a £100 switching bonus) when it came to the number of people switching their account to the bank.

It currently offers cashback on bills and some spending to 123 World customers and it is now offering all debit and credit card holders up to 15% cashback on spending on top of existing benefits.

Its 'retailer offers' are available to all new and existing customers who spend on their debit or credit card and are registered for online or mobile banking.

Santander says it tailors cashback to retailers suited to customers on an individual basis. When a few Santander customers in the office checked their accounts they found six offers, including: 5% at Waitrose (max £10), 8% at New Look (max £30), 15% at Hungryhouse (max £30) and 15% at Heals, Hertz car rental and Spafinder.

MSE forum users have reported being offered cashback at Starbucks, Homebase and Argos.

The new cashback offer is in addition to the list of rewards Santander 123 current account customers already get, which includes up to 3% cashback on various household bills.

Its 123 cashback credit card gives 1% cashback in supermarkets, 2% in departments stores and 3% on rail travel or petrol fill ups (max £9/month).

However, both the 123 World current account and credit card come with a £24 annual fee, although the fee for the credit card is waived for the first year if customers also have a current account.

How do I get the cashback?

To get the cashback you need to register for online or mobile banking with Santander to activate your specific offers. If you haven't registered for online or mobile banking then you won't be able to get the cashback offers.

Once you turn on your offers, you'll be given a selection of retailers and you'll need to select which ones you want to earn cashback on. Once selected, just spend on your Santander debit or credit card in the selected stores and the cashback will be credited to your nominated Santander account the next month.

The number of deals offered varies by customer but cashback offers typically last 4-6 weeks, after which new ones will be added to your retail offer account, so check regularly to see what new cashback deals you could get.

What if I don't have a bank account or credit card with Santander?

If you don't have a bank account or credit card with Santander you won't be able to get this cashback offer.

However, don't just take out a Santander bank account or credit card to get this deal, check if you can earn more elsewhere. Lloyds, NatWest, RBS and Halifax, for example, also offer cashback rewards to their debit and credit card customers when they spend in certain stores.

Halifax and Lloyds offer up to 15% cashback at some retailers, although as with Santander, account holders need to log into their online banking to select their specific cashback offers.

NatWest and RBS current account customers, meanwhile, can earn up to 1% cashback in certain shops if they join its Cashback Plus offer. Retailers include BP, Cafe Nero, Cineworld and New Look. Plus the banks also offer extra personalised cashback offers in the 'your offers' section in your online banking. Log in to find your specific offers.