The UK data can be found at ICNARC.
https://www.icnarc.org/Our-Audit/Audits/Cmp/Reports
This link opens a PDF download: https://www.icnarc.org/DataServices/Attachments/Download/c9b...
(17th April 2020)
> To date, ICNARC have been notified of 6664 admissions with confirmed COVID-19, either at or after admission to critical care, by critical care units in England, Wales and Northern Ireland. Of these, early data covering the first 24 hours in the critical care unit have been submitted to ICNARC for 6313 admissions of 5578 patients (Figure 1 and Figure 2). Of the 5578 patients, 2936 have outcomes reported and 2642 patients were last reported as still receiving critical care (Figure 3). The largest number of patients (1924) are being managed by the three London Operational Delivery Networks (Figure 4). Please note that Figure 2 and Figure 3 are affected by a variable lag time for submission of data of about 1-3 days (shaded grey)
[...big snip...]
> Critical care unit outcomes have been received for only 2936 (of 5578) patients, of whom 1499 patients have died and 1437 have been discharged alive from critical care (Figure 8 and Figure 9).
There's probably some more stats about critical care capacity here: https://www.england.nhs.uk/statistics/statistical-work-areas...