Cross-border patients are set to miss bowel cancer screening because of a mismatch in provision between England and Wales.
A Gloucestershire GP has warned that it is only a matter of time before a patient takes legal action for failure to screen.
The NHS in England uses GP lists to contact patients for bowel cancer screening, but in Wales, patients are contacted based on where they live.
Patients living in England but registered with a Welsh GP will miss out. Welsh residents registered in England will be called up in both countries.
Around 20,000 English residents have a GP in Wales and 15,000 Welsh residents have a GP in England. Patients in parts of south Gloucestershire are unable to register with a GP in England.
Mark Harper, Conservative MP for the Forest of Dean said in a parliamentary debate that 8,000 of his constituents are registered with a GP in Wales.
Tutshill, Gloucestershire, GP Dr Alasdair Jacks said: 'Once the roll-out of screening is complete, the next eligible person to develop bowel cancer could perfectly reasonably sue the government because it could have been screened for.'
Richard Winder, deputy director of the NHS Cancer Screening Programmes, admitted: 'A number of people are not currently being invited for bowel cancer screening. We are looking to update the IT system to identify those who are not registered with an English GP but reside in England.'
Health minister Ben Bradshaw said in the debate that the NHS was 'aware of the issue', and would 'ensure that nobody falls through the gap'.
NHS Gloucestershire said that 'all patients will have access to screening'.
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