From Wiki

A general guide to getting a UK passport can be found here.

The consulate has set up an on-line passport application status enquiry service for those with an urgent need to travel. However - the best advice is to not book travel until you have the passport in your hand.

In the US, go to here and in Canada, go here and click on the passports tab (you can also go to www.UKinUSA.fco.gov.uk/orlando and click on the regional information box).

Photos

• US sized photo's are ok, they'll get cut down to size at the Embassy

• Counter signature, this only needs to be done if you significantly look different from your previous passport or it is your first. A British person does not have to do the signature, just someone of standing such as a doctor, teacher, lawyer etc.
  

US Birth Certificates

• Many, if not all, US states allow an adopted person to apply for a new birth certificate showing adoptive parents as natural parents.

• An adoptive parent link does not confer automatic British citizenship (although child can be registered as British until age 18)

• Hence, the Embassy does not accept US birth certificates as proof of a link to a natural parent, unless the birth certificate was issued within 3 months of birth.

• If you have replaced your birth certificate, you will need additional evidence to show you were not adopted. This can include hospital records from when you were born. Alternatively, you may need to provide additional documentation from the state birth registry confirming that your birth certificate has never been reissued pursuant to adoption.

Misc

If you were applying for a first passport for your baby born in the US, you could also send in the application for a consular birth certificate at the same time if you wished, but this would be processed by the Consular Section of the Embassy in Washington.

You can include multiple passport requests/renewals in the same packet to save on return postage - BUT check each form very carefully as they will return ALL the packet even if only one set is wrong.

If you are renewing your passport and are including a recently expired or soon to expire GB passport in the same packet then you dont normally need to resubmit any documents (ie Birth cert).

The passport can be renewed at any time, but only any valid time remaining within 9 months or expiration will be transferred to the new passport.