Hipennine
You know this for sure then?
Yes working from home will be encouraged more but there is still the need for office space. Productivity is higher in the office overall in my line of work due to better opportunities for collaboration.
I know government are more interested in new builds so any move out of London will highly likely be into a new build where ever it is. Just look at the new regional centres in HMRC - some of the old offices had adequate space to become the regional centres but HMRC chose to have built band new facilities and the lease them.
So if they want it built a private developer will build it.