The global research response to the COVID-19 pandemic led to the unprecedented use of extremely large datasets based on linked electronic health records available within secure, privacy-protecting Trusted Research Environments. These include OpenSAFELY and the NHS England Secure Data Environment, each of which includes linked data on more than 50 million people. In addition, the NHS is embarking on an ambitious initiative to build several sub-national secure data environments which will host detailed secondary care, imaging and genomic data, linked with primary and other secondary care medical records. Our team work across trusted research environments on several major programmes.