Jack Taylor wrote:

Absolutely. Unfortunately, it isn't just a case of spending money
on restoring the through lines, as it would be at places like
Beaconsfield. In BR days (as at Gerrards Cross) the entire alignment
was slewed in places, meaning that, in addition to the restoration
of platform loops, most of the construction at platform level of
Sudbury Hill, Harrow would require demolition and reconstruction to
meet current HSE requirements with regard to platform widths etc etc.

Maybe, maybe not - at worst the entire platform surface would need to
be demolished and rebuilt. Considering the poor state of the platform
furniture at Sudbury Hill, Chiltern may simply choose to knock it down
and build a new platform on top of the old, a la Risborough.
Cooperation from TfL (i.e. buses) would be needed in order to ensure
that the expensive works actually had people taking advantage of them.

The present costs of such work would be prohibitive for such a
(currently) lightly used station - and accountants are not renowned
for basing their investment on projected figures, which is why so
many far better projects that can be seen to be needed (to anyone
with a basic understanding of railway infrastructure, operation,
local passenger flows etc.) have not been given the go-ahead without
the financial commitment of local and county councils.

Would such approval from the London Borough of Harrow be difficult to
secure, given the stereotypical dislike of the Underground?

In almost every case nationally, where the bean counters have
restricted the development of new stations and routes and have scaled
down the expenditure, the coffers have had to be reopened within a
couple of years for infrastructure improvements because ridership
has far exceeded projections and capacity problems have ensued!

Indeed. I would think though that rebuilding Sudbury Hill with through
lines could be costed at far more than a 'local' level - the
flexibility improvements to services from the Chiltern routes, with the
subsequent increases in reliability and possibly even income, could
also be considered in favour of approving such a project; TBH though I
know little of such things ;-)