If you intend to marry in the UK:
1. Apply for certificate of approval (CoA).
2. When CoA is received, get married in the UK and register the marriage.
3. Apply for further
leave to remain as spouse of British citizen.
Please note that a CoA is not an immigration document that allows you to stay in the UK beyond the expiry date of valid visa. Therefore, you must apply for CoA well in advance so that you can marry and apply for further leave to remain before any valid leave (visa) expires.
If you intend to marry outside the UK (e.g.- Thailand):
1. You don't need a Certificate of Approval if you do not intend to get married in the UK.
2. Register your marriage as per laws of the country in which the marriage is solemnized (e.g. - Thailand)
3. You may then apply for
entry clearance as
spouse of British citizen,
or (if your Tier 1 (PSW) leave is still valid at that time) return to UK as Tier 1 (PSW) migrant and then apply (from within UK) for
leave to remain as spouse of British citizen.
regards