Upvote:1
You should have no problem leaving the Netherlands going to the UK if you already hold a UK visa.
There is no separate document needed to exit the Netherlands.
You could still be refused entry to the UK if there was a problem with the visa such as a significant change in your circumstances after the visa was issued. This is uncommon though
Upvote:2
No you donβt. If you have a visa for U.K. you can go there from anywhere as long as you have all the applicable transit visas.