For the lump sum L, the calculation is relatively simple: you should calculate your net worth today in today's money, and since L will be uprated with inflation, its value today is also L, at least if you ignore any caps on the uprating and you accept that the inflation measure they use (probably CPI) is a fair estimate of the inflation in your own living costs.
For the rest, the way to value it, as you suggest in the tags, is to compare it with an equivalent annuity. There are some tables online here and here, though none for the exact equivalent scenario of both "joint life" and "index-linked". In any case the exact rates you could get would depend on the age of your partner relative to you, the age of retirement and your health at the time of retirement, as well as changing over time before you actually retire. So you'll only ever be able to get a rough estimate.
At a very rough guess if you're looking at age 65, I would put it at about 3-3.5%, i.e. I would multiply the initial payment by about 30 to get a capital value. Again given the inflation uprating between now and retirement age, you just need to think about the present level of the pension to do the calculation.
There are also various online forms you can find by searching for "annuity calculator" that you could use to get a more personalised illustration, but you'll need to push your age forward and also hand over your personal details.
Another thing to bear in mind is the risk of the pension not actually being paid in full, particularly if it's with a quasi-state scheme with a significant deficit (e.g. the Universities Superannuation Scheme), rather than with the government itself. There's at least some risk of a scheme going under before you retire and falling into the Pension Protection Fund, which would leave you with less income and less good index-linking than expected, or even worse for the Pension Protection Fund itself to fail entirely. Even with the government, if there was a serious enough financial crisis they would probably partially renege on their promises. So you should maybe reduce the notional capital value by some percentage to account for this risk.
All that said, when I think about pensions and net worth, I actually think about this the other way round: I have a defined contribution pension and I look at annuity rates from the perspective of whether the pot will give enough retirement income to live on comfortably, rather on its absolute value today.