Company seals were traditionally used to lend official status to the documents of a company, signifying that the document was an act or deed of a company. In the past, a seal was used to make an impression on melted wax applied to the document. Modern seals generally take the form of a rubber stamp. There is no legal requirement for a company to use an official seal, though many companies do for documents which need to be executed as deeds, and for share certificates.
Coddan offers a company seal as an optional extra. A company seal can be ordered from Coddan at the same time as you order your company formation, or as a stand alone service.