If you need to file confidential information relating to a published application or patent at the UK Intellectual (i.e. Patent) Office, you must make a request for confidentiality at the time of filing the document containing the information.
Rule 53 allows a request for confidentiality to be made on filing the document or up to 14 days after this date. However, due to the electronic filing systems of the UKIPO, any confidential document not accompanied by a request for confidentially will be open to public inspection until a request is made.
This was set out in a Practice Notice issued in April 2007 (see page 42 of this document):
From 1 April , any document filed in connection with a published patent application or a patent is open to inspection on filing. However, it remains possible to make a request for confidentiality at the time of filing the document. If such a request is made, the document is kept confidential while the request is considered. It also remains possible for confidentiality to be requested up to 14 days after the document has been filed. The document will have been open to inspection in the meantime, but will become confidential once a request has been made and will remain so while the request is considered. The 14 days for making a request continues to be extendable at the comptroller’s discretion.