are you building the leisure centre or maybe smashing/mixing up concrete/hod carrying/testing running machines/weight lifting etc ie physical work for 12hrs @ 40min break is legal but you could collapse before that.
In your case maybe it means you can only leave your post for 20mins (toilet etc). You can eat/drink at your desk.
As receptionist in health club you take income from punters to pay your wages.....you're in best position to assess whether employer can afford you more time off by the income less exes.
It must be different in some jobs then, I work 9am -6pm and get 2x 20m paid breaks and an unpaid 1hr lunch break, do you work your weekly contracted hours over just a couple of days then?