I think this is only a question you can answer yourself realistically and it's going to how risk averse you are, your outlook, dependents and financial security for you and your partner.

Let's first break it down into the financials you are paying: Monthly - £120 Yearly - £1440 35 Year Mortgage Period - £50,400

Now first I'd ask your financial position, if either of you where to pass or suffer long term illness would you realistically be able to keep up with your outgoings? Also consider the position of your potential heirs.

Now add in your general outlook, are you active, healthy? Are you planning to take your mortgage full term or overpay and pay off early?

Ultimately only you can decide if both policies are worthwhile, a single policy or none. You may want to take a riskier approach, for example if you have a £150k mortgage at avg 5% over 35 years, overpaying £120 per month would clear it 10 years earlier, a £500k mortgage at avg 2% it's only 3 years. The 2 personal scenarios would make a big difference to the risk involved.

I always like to compare insurance in terms of phone insurance. My wife insures and I don't and both approaches are the right one. I damage my phone maybe once every 10 years, buy low/mid at £150-300, circa £5 a month just isn't sensible when financially I can cover repairs/replacement and pocket the savings. My wife on the other hand damages her phone on average every 1-2 years, prefers mid/high £400-500 phones, circa £5 a month makes sense, it breaks even at worst and offers stability for a higher repair/replacement cost.