If the thought of being in debt stops you sleeping at night or you'd rather have a sure thing than the chance of a big win, here is an alternative investment plan. However, you should know that although the returns will be safer, they will almost certainly be lower than the standard plan.
Save one month's expenses in a current or instant-access high-interest savings account. [This will weather any problems like car repairs, unexpected bills, payroll problems, etc. You should be able to get hold of the money at any time. Note that it is one month of expenses, not income.]
Pay off high-interest debt. [Guaranteeing that you won't have to make those future interest payments! Compounding works both ways.]
Save a six-month emergency fund. [This could be in something slightly harder to get at, such as premium bonds or a notice account, but should not be in stocks and shares. If you lose your job or have to stop working temporarily, you will have six months of expenses saved before you run out of money, giving you time to either find another job or arrange to draw down your other investments.]
If you are under 40 and want to buy a home, max out the LISA allowance, investing in index funds. [You get a guaranteed match from the government in addition to the tax benefits of saving in an ISA. If you don't want to buy a home but are not interested in very early retirement, you may want to do this anyway as you still get the match and can access it at pension age.]
Contribute to your workplace pension up to the employer match. [The match is guaranteed additional money!]
Pay off lower-interest consumer debt. [Excluding mortgage and student loans.]
Now that you're debt-free apart from your mortgage and student loans, sit down and have a chat with yourself about your feelings about debt and your plans for retirement.
If you:
a) get cold sweats at the thought of your mortgage, pay it off. Then invest in a SIPP first if you're aiming for a traditional retirement and an ISA first if you're aiming for an early retirement.
b) feel slightly apprehensive about your mortgage but kind of OK about it, put half your extra cash towards your mortgage and half in a SIPP first if you're aiming for a traditional retirement and an ISA first if you're aiming for an early retirement.
c) feel totally blasé about your mortgage and regard it as healthy debt, put all your extra cash in a SIPP first if you're aiming for a traditional retirement and an ISA first if you're aiming for an early retirement.
If you have such a vast firehose of cash that you've maxed out your workplace pension, your ISA, your SIPP and paid off all your consumer debt and your mortgage, invest in taxable accounts or rental property, depending on your interests and area. Only at this stage, even for the highly debt-averse, should you even consider making additional payments towards your students loans. Interest rates will always be minimal, repayments are linked to income, and they will be forgiven after 25 years. You should only think about paying them off before now if you are literally crying yourself to sleep over them every night.