I disagree with everyone else, I think income protection is very important if you want to be able to maintain your current standard of living if you were to become permanently unable to work.
If you have good sickness benefits then you can tailor your cover to start paying out once your income stops, which means that you monthly premiums would be lower than if you were to have it pay out sooner.
Yes they only pay a % of your income, but it is typically a maximum 60% of your gross earnings, which is not taxable so actually you wouldn't be that much worse off than you normal net income.
You would also need to make sure that you continue paying into a pension whilst claiming as the benefits usually stop once you reach retirement age.
What the adviser probably meant when he said you get a preferential rate when your older, is that the premiums are based on your age and health when you apply, and won't go up when you're older, so it's best to apply now while you're young and healthy.
As far as saving instead is concerned, just say that your premiums for the policy were £50 per month, but you save that instead. If you were to need to claim in 5 years time, you would only have accumulated £3000, but you're not going to be able to live off that until you retire.
Just do read the small print and go to a trusted big name. Read up on claim statistics and don't be put off by people saying they don't pay out. They do if you have a valid claim, and I have seen it first hand.