A high-security prison's effort to tackle its serious drone problem is being frustrated by heritage concerns over installing grilles on its Victorian windows. HMP Manchester, a Grade II listed building, wants to make it harder for drones to deliver drugs by fitting cell windows with 'impenetrable' security barriers. A previous inspection found prisoners at HMP Manchester, commonly known as Strangeways, had been using filaments from their kettles to burn through plastic windows to facilitate drone deliveries. However, attempts to install new security grilles have seemingly become bogged down by heritage concerns relating to the 158-year-old listed building. Last year, Greater Manchester Police said more than 500 mobile phones - mostly iPhones - and SIM cards were seized from inmates at HMP Manchester.