I've just had a look on the Land Registry site and looks like it might be a Form K Restriction (the LR have a number of standard ones for use in different situations -
http://www1.landregis...andard-restrictions):
Form K (Charging order affecting beneficial interest - certificate required)
No disposition of the
[choose whichever bulleted clause is appropriate]
•registered estate, other than a disposition by the proprietor of any registered charge registered before the entry of this restriction
•registered charge dated [date] referred to above, other than a disposition by the proprietor of any registered sub-charge of that charge registered before the entry of this restriction
is to be registered without a certificate signed by the applicant for registration or their conveyancer that written notice of the disposition was given to [name of person with the benefit of the charging order] at [address for service], being the person with the benefit of [an interim or a final] charging order on the beneficial interest of [name of judgment debtor] made by the [name of court] on [date] (Court reference [insert reference])