I agree with Baracuda's advice, but it is worth warning you that there is no easy answer to the question, and a pensions adviser may not be in a position to give much useful advice unless he/she knows a lot about the scheme.
If the scheme is fully funded, then the decision is pretty straightforward. If it is underfunded, your value has been written down to reflect this. In this case, it would be a good idea to stay put if the employer (and/or the current employees) were likely to agree to a recovery plan which would mean that over time, the write-down is likely to disappear. On the other hand, if a recovery plan is unlikely, it is possibly a good idea to get out now if the situation is going to get worse. Just to complicate things further, the Governement is considering a change to the law (but have not made a decision) that could see members of underfunded schemes who have not yet retired do a bit better, i.e. not suffer quite as big a write-down.
It would be worth trying to get what information you can from the scheme trustees about the current situation and some kind of feel for where it is going.
d