1. Does your employer contribute to the pension scheme?
2. Depends on your attitude to risk. If it's a unit linked fund you are not locked in for 5 years but your capital is at risk. If it a tracker bond with your capital guaranteed after 5 years, personally, I would not touch it.
Start at the end and work out how much you will definitely need. I assume that you are going to be saving over the next 5 years on a regular basis so factor that in to what will be required. You can then decide if you are in a position to take a punt on equity/property asset class with SSIA money.