He works an average of 20 hours a week. He won't be working any hours during their trip to india (1-2 weeks) therefore he has to make that up elsewhere, meaning some weeks he'll be working 30 hours a week.
The "average" has been conveniently and quietly dropped from the discussion by the press in order to make him look worse.
Also lost, by those who want to compare his workload to a person driving a desk for 40+ hours a week, is that it isn't driving a desk.
There are 8 pilots on the Cambridge EAAA base, and 20 hours of shift time a day (2 10 hour shifts), ~30 days a month. That's 600 hours, minimum, shift time; if all pilots were working the same amount, that would be 75 hours of shift time each per month. We know that some flights have two pilots, but "most" do not. So let's assume 1/3 of the shifts are covered by 2 pilots; that's 800 hours of available work. Divided by 8 pilots, that's 100 hours a month.
Complicating it slightly is that they have both full and part-time pilots. The full-time pilots work 30-32.5 hours a week according to the Telegraph.
No-one is working 40 hours a week at that job.
Is he working fewer hours than his full-time counterparts? Yes. But so are the other part-time pilots.