Ancestry has added the London Gazette to its list of browsable collections. The 306578 records can be browsed by publication date, month or year.
In this format, it will no doubt have its uses, but most family historians will find the free, fully indexed London Gazette website more useful as it can be searched by any keyword, including name.
The London Gazette is the UK's official newspaper of record ie it publishes data from a range of official sources. It holds notices of bankruptcy and civil service appointments and promotions, details of military appointments and promotions and despatches from the War Office, notices of legalised name changes and of deaths and executors. It can be extremely useful for all manner of detail. And it's free to search and view.
To give an example from my own research, the early careers of my grandfather's two brothers can be tracked through the newspaper. From the family's labourer's cottage in Clonakilty, Co Cork, they travelled to Dublin in the last years of the 19th century to sit examinations for appointment to the Post Office, then part of the Civil Service. Their successes were recorded, as were their subsequent postings to London as Boy Clerks. Later promotions to GPO Sorters were also noted. Another brother is recorded for the award of the Meritorious Service Medal at the tail end of WW1.
The Edinburgh and Belfast Gazettes can also be searched via the London-Gazette website.