Can you give an example set of numbers where you have two loans and it is better to pay off the lower interest rate first?

Yes. Where the low rate term is coming to an end in 6/12/18/etc months time and the rate reverts to (a higher) SVR. We have no idea if this may be the case. We’re just assuming it isn’t. What’s that saying about assumptions..?

There is no need to look at a calculator as the way you are using one is wrong.

Instead of comparing costs over the life of the mortgage (because as ampthill pointed out… it means you’ve assumed the overpayment won;t be transferred once one is paid off), use the MSE calculator and sum the total loan value of the 2 mortgages after say a 5 year period (before the pay-off & transfer would matter).

If you assume a 25 year repayment period for each, after 5 years:
Overpaying on the smaller mortgage = Total debt of £197,990
Overpaying on larger mortgage = Total debt of £198,103 (+£113)

From this you can see that total debt is reduced more quickly by overpaying on the smaller (higher interest) mortgage.
The effects of compound interest only makes this more pronounced as if we look at the values after 10 years, the difference is even greater:
Overpay smaller = Total debt of £140,977
Overpay bigger = Total debt of £141,486 (+£509)

Yes. Where the low rate term is coming to an end in 6/12/18/etc months time and the rate reverts to (a higher) SVR. We have no idea if this may be the case. We’re just assuming it isn’t. What’s that saying about assumptions..?

Even then, he would be better off overpaying the smaller loan until the time at which the larger loan reverts to the SVR.

The total sum of debt makes no difference to the choice you make.

FFS go to your mortgage lender and ask. They will work it out for with full facts, current mortgage terms, repayment methods, may consider rates end dates. I am sure people who do not deal with finances let alone mortgages every day are giving you “advice” read opinions.

Ignore my SVR comment. I was assuming that you could effectively offset savings from one, into the other after the SVR goes up… which would be possible through payment holidays etc but makes it all the more complicated.

Double post.