BHRUT joined the Oracle Millennium system, which Barts Health NHS Trust already uses, at the weekend (8-9 November).
Information about diagnoses, procedures, medications, allergies and test results for about 10m patients will now be held in a single secure digital form, quickly and easily available to all healthcare professionals involved in any patient's care.
Clinicians will be able to share details of any patients that need to be transferred between any of the seven hospitals run by the two trusts.
For some months a specialist team Barts Health's informatics department has helped prepare for the handover.
Matthew Trainer, chief executive of BHRUT, said: ‘As a digitally immature trust, we've relied heavily on the experience of Barts Health and on learning from other trusts who've introduced one.
‘It's clear that our transition from paper to digital will be bumpy and visitors to our sites will have to be patient as all of my colleagues get to grips with EPR.'
Daniel Phillips, director of clinical systems at Barts Health, added: ‘BHRUT joining our Oracle Millennium system is part of a multi-year collaborative programme of digital transformation.
‘We do not anticipate any disruption to Barts Health and all systems will remain accessible.'
As the last NHS trust in London to move away from paper records, BHRUT will also introduce electronic prescribing.
However, the move doesn't yet cover maternity or pathology services, so there is still scope for further collaboration. Within north east London, Homerton Healthcare also use a version of Millennium, but as yet there are no plans to link up.
Barts Health holds records for more than 8m patients on Millennium. BHR had 2.5m paper records, of which 1.8m were already replicated within the Barts system.
Charles Gutteridge, chief clinical informatics officer at Barts Health, said: ‘This is an amazing opportunity to work together on improving population health for north east Londoners. Everyone will benefit from better use of data, AI applied to health information, and cutting-edge research.'
