GP premises — switching from notional to cost rent, has anyone done this recently?

Our lease is coming up for renewal next year and the district valuer's notional rent assessment came in significantly lower than our actual market rent. We're considering a switch to cost rent. Has anyone navigated this with NHS Property Services or a private landlord recently? I'm told the process is much harder than it used to be and that NHSE are more difficult to deal with. Would love a realistic view of the process.