Section 187 of the Patents Act 1990 requires details of changes in ownership of patents to be recorded on the register.
However, there is no penalty imposed on a patentee who fail to record changes in ownership or entitlement.
Nevertheless, you can't sue anyone until the real owner is recorded on the register.
If you miss an official deadline and the current owner is not recorded on the register, then the current owner is likely to be barred from claiming that they missed the deadline due to an error or omission.