I echo CM's advice...it only used to be ten quid, which is a good investment.
However, there are essentially two ways this can be done, depending on the agreement of both parties and the complicity of the court (which is different between England/Wales & Scotland).
The way I did it (in Scotland) was to have it valued by an actuary and then split according to Scottish Family Law (based on 50/50 of value accrued during the marriage term).
Downside of this is you will have to front up with a cash sum, which can be considerable. Upside is that your ex will give up all rights to any part of your pension in the future.
The other way is to have a part of your future pension allocated to your ex. Upside, no need to find a large sum at the point of divorce; downside you'll only get a proportion of your pension when you retire.
I'm not sure if both these options apply in England. Then again, there is huge inconsistency in family law courts anyway and more often than not the judges interpretation plays a big part. Therefore to add to CM's advice about the pension society...whatever you do, if at all possible, keep it friendly and only use solicitors and courts to sign off agreements you have already made.