as was state in your approval letter i attach the advice from the home office site
Arranging the ceremony
When you receive your invitation to a ceremony, you have 90 days to attend one. Your invitation will include contact details for the local authority that will arrange your ceremony. The ceremony usually takes place at a register office.
Most local authorities arrange group ceremonies for everyone in the local area who is becoming a British citizen at that time. You will usually be able to take two guests with you to the ceremony. Attendance at the ceremony is by invitation only.
You can arrange a private ceremony. You should discuss your requirements with your local authority. You may have to pay an additional fee to arrange a private ceremony.
this below may also help as you can see it's not worth missing the ceremony as you can see below which i got from the UKBA website for advice to the IO
6.11.8 Where an applicant is required to take an oath of allegiance he must normally do so within the time limit of 3 months prescribed by the British Nationality (General) Regulations 1982 (or the British Nationality (General) Regulations) 2003, as appropriate). Otherwise the applicant cannot be registered or naturalised unless the Home Secretary decides to extend the period.
39
6.11.9 When a request for the taking of an oath of allegiance has been sent, the file should be almanacked for 1 month and a reminder letter (OATH-REMINDER) sent with a new oath form if the original oath form has not then been received. The letter makes it clear that an oath should have been taken within 3 months and allows a further two months for it to be completed and returned. The file should be almanacked for 2 months.
6.11.10 If the applicant asks for an extension of time and gives an acceptable reason (e.g. a serious illness), an extension of up to 3 months may be allowed (or whatever longer period may be justified by the reason given for the request).
6.11.11 If an oath is returned undelivered, or not returned within 3 months of the original request, the applicant should be informed that it will not be possible for him or her to become a [British] citizen because the Home Secretary is not able to register or naturalise a person who has not taken an oath. Stock letter OATH REFUSAL (NON RECEIPT) should be used.
6.11.12 If the applicant still wishes to become a [British] citizen, and had an entitlement at the date of application, we may issue a certificate at any time on the basis of the original application on receipt (if necessary) of the fee prevailing when the application was made and an oath of allegiance. In all other cases the applicant will need to re-apply under an appropriate provision