I would ask a company like http://www.skyreachrelocations.com/ . They should be able to answer questions like yours as they help people move from NL to UK everyday.
Have you lived with your Dutch partner in the UK (or any other country) for 6 months or more?
If yes, can you prove it? Things like shared bank account statements, tenancy agreements, any documentation with both your names on it are good.
You will need to fill out the form Application for Verification Against Community Law. You will also need some documentation like your birth certificate (with an Apostille or similar), your marriage certificate to your Dutch partner (or Certificate of Single Status from your country of origin - with Apostille).
Take all this to IND on the day of your appointment. The application fee is 41 Euro.
If you have not lived together in another country, you will need to apply for residency based on family formation with a Dutch partner. This involves gathering a lot of the same documentation, as well as his financial details (he needs to earn more than 1500 Euro per month on a contract of more than 12 months).... The application fee for this process is 830 Euro for you, and 188 Euro for additional family members - for instance if you have a child.
Yes, my partner and I have a civil partnership and met in Holland. We have been living in the UK since Nov 2009, but might need to move back to Holland due to a family matter.
I am aware that when my partner and I travel together I do not need a schengen visa and that because we have lived together outside of Holland in a Europe Union country and he has practised his treaty rights he now falls under European law. Therefore we are able to move back. I was unsure about how would go about it. Thanks for you post they are helpful and I will look into this.