It's interesting that of the four current directors of Plusnet, the CEO and two others are not on Plusnet's payroll. They are still paid by British Telecommunications plc.
Andy Baker's "salary and associated costs" are paid by the above and refunded by Plusnet. The other two are apparently not paid extra for their PN duties so no charge for them.
The fourth director, appointed in April 2016 is presumably head of the finance area, as she is a chartered accountant. Who pays her is not obvious, as her correspondence address is the same as all the others, BT Centre, 81 Newgate Street, London. Not Plusnet, Sheffield any of the four. She may have the same arrangement as Andy Baker.