UPDATED April 2019, They have been closed for over a year to new unagented submissions. I am leaving this here for reference only, but removing them from the yearly manuscript guide, and from the updated SF publishers list.
Gollancz is an established UK-based publisher of science fiction, fantasy novels, and horror novels. They only publish worked aimed at adults. They have good distribution within the UK and have excellent covers.
Gollancz is open to the unsolicited submissions of manuscripts on a rolling basis. They consider submissions regardless of the author’s location and country of origin, as long as they are written in English.
All submissions must be made through the post to be considered. No email submissions of any kind are allowed.
What is particularly notable for a major independent publisher is that they accept work that has been previously self published, as long as the author currently holds all the rights.
When you submit send a covering (cover) letter, one-page synopsis and a printed copy of the first 50 pages of your novel. The sample should be 50 single-sided, double-spaced pages in standard fonts, nothing hard on the eyes. If the last chapter ends on page 48 or 52, use common sense to find a good break point.
They do not mention requiring a self addressed and stamped envelope so I assume they notify submitters via email. They do not return manuscripts under any circumstances so make sure that whatever you send them is just copies, and that you have the originals. Make sure you include your name, address, and email.
Novels must be at least 75,000 words in length. No upper word limit is mentioned. They are not interested in short story collections or novellas.
Their current goal is to respond to all submissions within three months of receiving them.
To learn more, please visit their website here. To check if they are open to submissions keep an eye on their news page.