Just to be clear, you have obtained indefinite leave to remain in 1998 and this is noted in your passport.
If you obtainined ILR on the basis of a workers visa then you wil have to apply for a naturalisation as a UK citizen before you are able to apply for UK passport.
The criteria for this is as follows:-
You must also meet the residential qualifying criteria, which means you must have been resident in the UK for the 5 years preceding the submission of your application for naturlisation and also:-
Provided you meet the above and evidence appropraitely with supporting documentation then you will be granted naturlisation. You will have to apply to the UKBA by completing form AN which is available for download with the guidance notes from the UKBA's website:-
A solicitor would be able to prepare the application for you for around £600-900 + vat, you can find Uk immigration solicitors through the following Law Society Website search engine:-
Once you have obtained UK citizenship you will be able to apply to the passport office for a UK passport.
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