The star, who has played Charlie Fairhead on the medical drama since its inception in 1986, was one of those named when the salaries of those earning over £150,000 at the corporation were made public last week.
The report showed he took home between £350,000 - £399,999 last year, putting him ahead of more high-profile stars including ‘EastEnders’ actors Danny Dyer, Lacey Turner and Adam Woodyatt, as well as Doctor Who’s Peter Capaldi.
Tom has now claimed Derek has earned his hefty salary due to his length of service, telling The Sun: “It’s like being a footballer — you earn your credits. I’ve just done six months on ‘Casualty’, but Derek has done 31 years of service.
The Radio 2 Breakfast Show host was revealed as the top BBC earner, taking home at least £2.2million a year.
The publication of the documents also showed a sizeable gap in the earnings of the corporation’s best-known male and female presenters and actors.
Many of the BBC’s female stars have since signed an open letter to director general, Tony Hall, demanding the corporation tackles its gender pay gap immediately.
The BBC has claimed it aims to address the problem, with a spokesperson saying (via the Press Association): “We have made significant changes over the last three years but need to do more. Tony Hall has pledged the BBC will go further faster.
“We are committing to closing it by 2020 - something no other organisation has committed to doing.”