What are the risks associated with long term investments?

What are the long term risks in investing in shares, buying property or paying regularly into a pension scheme? Which is the most financially secure?

You need to get a financial advisor, regulated by the financial services authority of course.
The problem with investments is poor returns.
Property development has worked for some people.
Pension schemes are becoming more popular, but you need to fnd the right one for you.
As I said before, you need an IFA.

The longer your time-frame, the harder to predict.

The answer is probably a) buying shares because stock markets can decline say 40 - 50% in a couple of years - see NASDAQ at 5000 + . Property may have declines but it doesn't move down that much ( excepting vacation homes and swamp lands) - single family residences are the safest property investment.
Pensions are safe if there is a trustee watching the nest egg and it is a defined benefit plan i.e. the amount is guaranteed by the company or government agency. If it is a defined contribution plan like a 401K then you funds are safe if you diversify across the range of investments offered.

Rael estae has done well over the long term and also mutual funds