To get a half decent pension when you retire, you should be looking to be putting at least 10% of your salary into a pension. The later you start, the greater that percentage figure needs to be.
Assuming you will work until you are 70, you will only have saved a total of �41,000 � at today�s value (assuming your employer increases the payments with inflation). Hopefully, with investment the value would have grown. But I reckon you would be doing well to end up with a pension pot valued at �100,000 (at today�s value). This will buy you a fixed pension of around �7,000 per year.
On top of this figure, you should receive a basic state pension � currently around �5,000.
You will then be living on around �12,000 per year (equivalent value today).
Should all this come to pass � the biggest winner will be the State � who will not have to pay you means tested benefits. However, given that the pension payments are gratis, I would take up the offer from your employer � having a look at what is on offer here.
http://www.fsa.gov.uk/tables
The best hope I can offer you is that on retirement you can take 25% of your pension pot tax free, so you could be looking at �25,000, plus a small pension.
Personally, I would not add any of my own money to such a scheme � which I think would benefit the State more than me.