When I was 8 my mum and step day got married, my step dad was in the army and we were all due to get posted to Hong Kong for 2 years just a week after the wedding. We all went to the passport office so my mum could get a new passport in her married name in time for going to HK. I am 26 so at that time children were included on their mothers passport and I was included under my step fathers name "Fergus" as this is what I'd now be known as- the passport office agreed to do this. My name was not changed leagally from Smith to Fergus. Since then everything is in the name of Fergus including medical records, education, passport, drivers licence. I had to write a covering letter with my passport application explaining why my name was different to that on my birth certificate "Smith" I just explained to them that I am known as Fergus with everything to do with my life and from there I could get everything else using my passport as ID.

Here comes the problem- getting married next year and my birth certificate is required, however I want to get married under the name of Fergus as I will need a marriage cert showing Fergus to Barnard (my married name) when changing legal stuff such as Bank , passport, drivers licence etc and I want to make it as least confusing as poss.

Is it possible for me to change my name by deed poll to Fergus- and then be married under that name? This will make it easy for me to then change all other stuff into my married name in the future.
Or
Do you have to get married under the name on your birth certificate

Please Help as I really don't know what name I should be getting married under.

Thanks