I think you might see it more clearly if there are some hypothetical figures. (As will be obvious the key will be the respective values of equity vs pensions.)
Former Marital home - £250,000 mortgage £180,000 so net equity £70,000
Your jointly owned home - £250,000 mortgage £150,000 net equity £100,000 - your ring fenced share £60,000 - so his share of the joint equity - £40,0000
His pension £300,000
Her pension £200,000
Joint assets are therefore (70k+40k+300k+200k) £610,000
Assume a 50:50 split as starting point £305,000
Her assets (70k+200K) £270,000
His assets (40k+300k) £340,000
So he needs to give her (305-270) £35,000 of additional assets which doesn't necessarily have to be cash - could be pension.
This is very crude as the value of future pensions is not as much as pound for pound against the value of a house and a judge may take into account that she has a few more years to make contributions to hers than your DP has. But its a pretty good starting point. Spousal is pretty difficult to get these days especially as she has no young or disabled children at home so can work full time. I'd suggest that your solicitor and his solicitor work from this sort of a start point.