This website will be your LIFELINE when applying for British Nationality -
http://www.ind.homeoffice.gov.uk/ind/en/home/applying/british_nationality.html? BOOKMARK IT because you'll be using it all the time.
Here are a few important points for you to get your started:
1. You want to use the forms for BN1 : British Citzenship. The form is called AN(New).
2. The application fee for Naturalisation as a British citizen on the basis of marriage to a British citizen is £214, which includes the £68 fee for the manditory citizenship ceremony. You'll be presented with a certificate which you take to the passport agency to get your beloved red booklet. If you withdraw your application or it fails, only the £68 will be refunded.
3. Its taking 7.6 months to process applications (!!!)
4. If youre married to a British Citizen you must have been in the UK for 3 years before you can apply for British Nationality (as you know).
5. On the day you apply (officially that is the day the Home Office recieves your application at their offices) you must have been phyisically present in the UK 3 years ago to the day. For instance if you qualified for citizenship on June 25 2004 but were out of the country on June 25 2001 to July 1 2001, you would have to wait to send in your application until July 1 2004 to meet the phyiscal presence requirement.
4. On the day your application is recieved by the Home Office you must not have been out of the UK (even if you were still in the EU) for more than 270 days. In the 12 months leading up to the day your application in made, you must not have been out of the UK more than 90 days. In unusual circumstances, such as compassionate leave or caretaking for an ill relative abroad, they'll consider allowing absences up to 300 days, sometimes more if you can show that you have established your family and a substantial part of your estate and meet all the other requirements.
5. On the day you apply you must be free from time restrictions. In otherwords, you have to have your Indefinite Leave to Remain. You do not need to have had this for 12 months before applying if you are married to a British Citizen.
6. If you intend to travel while you appliction is being processed (especially during the first 12 weeks) you should not send your original passport. Instead, send a notarized copy (a copy of each page signed by a solicitor to say it is a true copy of an original). It cost me £35 for this.
7. You do not need to intend to remain in the UK after you are granted citizenship if you are married to a citizen.
8. As of the 28th of July you have to show that you can speak english. LOL. yeah, I know. I'll tell you more about it when I know, right now the requirements are sketchy.
There are other requirements regarding crime convictions, good character, references etc etc. But for the most part those are the key points. It sounds like a ballache but it isnt really. Good luck!