A document can be Apostilled or "legalised" under the Hague Convention. It provides the mechanism by which a document issued in one country and be certified for use in another.
The process is quite simple with remote appointments available.
Once the document has been checked (or notarised in some cases), it will then be sent onto the Foreign and Commonwealth Office in London to be formally legalised.
The Apostille can be turned around:
By Wednesday each week (if documents are received by Friday)
2 days (Urgent Apostille Service)