OPeNDAP - Can be used for browsing the archive file system and interactive downloads. It’s also a scriptable interface (API) to the archive over http, allowing remote subsetting within IDL, Matlab. Python etc.
FTP - The File Transfer Protocol is very common and is a good interface if you need to automate your data downloads.
CEDA Catalogue - Browsing information about the datasets in the archive.
CSW Programatically interrogating the CEDA Catalogue using Catalogue Service for the Web - service API. You can also use this service to harvest the metadata using the OAI-PMH protocol.
Specific data set services
Tools to subset or aggregate data before downloading are available for some data. These are linked to from the catalogue page for that dataset.