Private.

There were some decent lateral transfer options in the Civil Service, but being stuck two grades below my establishment grade (was GEO5 as a confirmed HOD then), it would mean that I map over to a similar subgrade in a different scheme. If I took on similar or higher responsibilities compared to a school HOD, then I would continue being underpaid in my new ministry for a few more years.

Jumping ship means I immediately get the pay that my responsibility level deserves.