A treaty only helps when both ends signed
The apostille works as a promise between states. Each side agrees to accept a fixed slip from the other instead of running its own checks. Lithuania joined that agreement in 1997, and Britain was already inside it, so the corridor between them has been a single-stamp route rather than a chain of desks.
What lands back on your doormat
You get the paper you sent, with the mark fixed to it, and the two now travel as one item. The wording of your own paper is untouched; the mark speaks only for the signature and seal on it. Because document legalisation for Lithuania ends there, whoever reads the file abroad is reading a finished bundle rather than a work in progress.
That also shapes the order of your own tasks. Anything you want done to the paper itself belongs before the mark goes on, not after, since a finished bundle should not be taken apart. Get the version of the record right first, then send it once.
Slip on paper, or a mark you can email
Britain issues e-Apostilles as well as the physical slip, which is unusual and worth knowing about. A digital mark suits a file that will be uploaded, forwarded or filed by a body that works on screen, while the postal slip suits a counter that wants something to hold. The choice does not change what the mark means or what it covers.
Cost, post and the single office
One office covers the country and it works by post, so there is no queue in London to join and no appointment to book. The published charge is £45 per document by post, or £40 per document on the next-day route for a registered business. An apostille from United Kingdom to Lithuania carries no second official fee on top.
Timing follows the post rather than a foreign desk, which is the quiet advantage of a one-stage route. If you have wondered what you need for an apostille for Lithuania, it comes down to one signed public version of each paper, one charge per paper, and one trip through the post.