Should I Invest or Pay Off My Debt First?

Spare money and outstanding debt: the maths is not always obvious once a mortgage is involved. You list your debts with rates and your spare monthly amount; this walks the decision framework, the interest-rate crossover point where paying down beats investing, the value of a guaranteed return, and where an ISA fits. You get a reasoned order, not a gut call. For anyone juggling repayments and the urge to invest.

I have the following debts: {DEBT_LIST} (include type, balance, and interest rate for each). I also have £{SPARE_AMOUNT} per month I could put toward either debt repayment or investing. My mortgage rate is {MORTGAGE_RATE}% and I can access a Stocks and Shares ISA. Walk me through the decision framework for whether to invest or pay down debt first, covering the concept of the interest rate crossover point, guaranteed vs expected returns, psychological factors, and emergency fund priority. Then apply the framework to my specific numbers and give a clear recommendation.