England and Wales report hospital admissions differently. England reports confirmed COVID cases (including transmissions within hospitals) while Wales includes suspected cases. As a result, Wales numbers have always looked artificially high.
Here are the exact definitions (from the fine print in government briefing slides):
England data captures people admitted to hospital who already had a confirmed COVID-19 status at point of admission, and adds those who tested positive in the previous 24 hours whilst in hospital. Inpatients diagnosed with COVID-19 after admission are assumed to have been admitted on the day prior to their diagnosis.
Wales data includes confirmed and suspected cases, and is the number of admissions to the hospital in the previous 24 hour period up to 9am. The status of COVID/non-COVID is as at the time of reporting not at time of admission.