A suggestion, if you send your documents to Croydon could you not book your PEO appointment at Croydon then ask then to get the documents from the office when you get there. If you explain your predicament I'm sure they'll be understanding especially if your father is terminally ill. Perhaps ring up...

The OP has a valid British passport I take it therefore a certificate is unlikely to be issued as a British Passport is proof of right to abode. What you should have done is applied for certificate before getting the British Passport as certificate doesn't expire. You'll have to likely wait until yo...