Once your mortgage has come to the end of its deal period you'll be placed onto the current standard variable rate (SVR) as a Santander customer. There are no products that you can apply for just on SVR as even the tracker mortgages track the Bank of England base rate rather than the Santander mortgage rate.
The current standard variable rate for Santander Mortgages is 4.24% which is one of the highest in the mortgage industry.
Although an initial rate may sound enticing it's the standard variable rate you are placed on afterwards which may be the most important.
If your circumstances change between when you take out a product to when it gets renewed several years later then you may not be in a position to get similar terms. For example, if you lose your job or you have a child and one parent does not work any longer.
That's just the reason why lenders publish an APR because this takes into account the initial generally discounted rate as well as the SVR for the term of the mortgage loan.
Whilst the initial rates offered by Santander are actually some of the best deals in the industry and market place you should perhaps consider not only the arrangement fees that are now charged by all lenders, the repayment penalties if you decide to pay off your loan or have to move house but also the standard variable rate you may have to pay if you don't remortgage once your deal period has completed.
With so many products on the market it may be easy to choose the lowest headline rate but once you have added in arrangement fees and any additional charges the rates offered by all companies including Santander may push up the actual cost of the mortgage. Therefore it may be prudent to either use a comparison website and certainly to get professional advice to help your decision making process.