Children should be locked in school at lunchtime to boost the uptake of school meals and stop them eating unhealthy food, say Sunderland Tories.At some secondary schools, fewer than one in 10 pupils now pay to eat in their school canteen, despite efforts to improve the food on offer. City leaders want to see junk-food exclusion zones set up around schools to stop youngsters buying greasy lunches from burger vans instead of healthy school meals.Robert Oliver, a teacher and Sunderland Conservatives' spokesman on education, thinks the best approach is to introduce lunchtime lock-ins. Many secondary schools on Wearside now keep at least 11-to-13-year-old pupils in school, some preventing all but sixth formers from leaving the school gates at lunchtime – and Coun Oliver wants to see all schools adopt that policy. "My opinion is that, realistically, only lock-ins are going to make any difference," he said. If you look at the table of top-performing schools, they are all keeping pupils in all the time. Obviously I don't think that's the reason they're doing well – there are probably other reasons as well – but there's definitely a link."