Its not clear if the .uk will drop at the same time as the .co.uk, it could be that the .co.uk drops and at some point later that day or 7 days later the .uk drops.
All that is clear is, the .co.uk MUST drop first, otherwise the .co.uk owner could still renew.
The .uk won't drop. It was never registered. It will just be available to register via the epp create command. Up until that point the epp response will fail with a 'domain reserved', or something similar response. After the drop the epp will allow registration. Will make for a few interesting milliseconds no doubt!