A few things you need to do/find out.
Firstly, is the pension index linked, if so then ALL advice will probably be to leave it where it is as it will grow with time at a vastly higher rate than you would get investing it certainly at the moment.
If it isn't then you need to mention whether its contributory or not.
If it was contributory, then that part of your pension, the money you have paid in, is yours and should be cashable in at anytime, of course, by doing that, you will also lose the other part the company paid in or be able to take a small percentage lump sum before it comes to fruition.
If it wasn't contributory, then chances are you will only get a small percentage cash out of it, as you haven't actually paid any in yourself.
If you wish to transfer the pension into another pension then this might be possible, it depends if the pensions are similar enough for this to occur.
In all this, you MUST take professional advice, its a serious matter and come retirement age could mean a BIG difference to you or your family. Ask your provider for a statment and rules leaflet and then take it to an experienced pensions advisor.