Grosvenor are a dab hand at not falling into the enfranchisement machinery if they can help it.
Grosvenor do receive massive amounts of ground rent. Ground rent is valued of very high multiples anywhere between 2% & 3% I. E. 30-50x income. (this is due to the value of the right of forfeiture, but don’t need to go into it here)
Ground rent isn’t just a few hundred quid a flat, it can be upto 15% or even 20% of the occupational rent, which in Mayfair can be well over £1000/m2 (£100psf for us oldies) for offices. Though more often around 5%.
Grosvenor retain the development rights on their land through the headleases, meaning If a building owner (lessee) wants to redevelop for higher value, the price of permission can be quite high.
Arguably it is a very valuable Estate precisely because of the Grosvenor family, not in spite of it. They “curate” Mayfair making it exclusive, timeless, stable and attractive for v high value occupiers.
Here’s a crude sum :
Total office stock in Mayfair is somewhere between 1m and 1.5m m2, and the average value m2 is £30000,the gross asset value of all the office buildings in that area is £37,500,000,000
Add to that, c. 5000 residences averaging, say, 200m2 each, and £30000/m2 value, that’s another £30bn.
And I’m probably substantially underestimating.