Ivor is correct.
'Straight ahead' is defined in MATS Part 1, which is, of course, intended for reference by ATCOs.
For aircrew, 'Straight Ahead' is similarly defined in CAP413.
Neither 'Runway Heading' nor 'Runway Track' appear in CAP413.
Take back what I wrote, I shall remonstrate with said Farnborough operative.
'Straight Ahead' it is, then. Track it is too, a heading it is not. Pretty conclusive.