how to snowball fixed loan???

Assuming the student loan comes from SLC, I would not overpay it but save up in a high-interest savings account instead. The rate of the student loan is in line with inflation so you will only pay back what you borrowed, in real terms. You can earn more interest on any given amount in a good savings account than you would save by overpaying that equivalent amount towards it.

The M&S card is very low interest so for that also I would recommend saving rather than paying it off more quickly than you have to (though keep an eye on the APR in case they increase it).

If you overpay these two, you will be debt-free quicker but you do actually lose some money on potential interest, and you lose liquidity - once you've paid towards a debt, you can't get at that money anymore. Plus at some point you may want to take out a mortgage or something which will undoubtedly have a higher interest rate, and it pays to have savings in place to minimise any amount that you might need to borrow later. I would build up savings first so that you have that liquidity.

It's a shame you can't overpay on the Tesco loan as that really is the only one of them where you're not likely to be better off by saving the equivalent amount. But if you save cannily in good accounts you will minimise your losses and be able to pay off the whole sum at once sooner.

(by the way, remember that student loan for this year is 4.8% not 2.4% - but even so, that is only for one year after which it is likely to go back down, and there are several savings accounts out there with higher net interest rates)