A historic atlas of Britain is being published online for the first time, showing how ancient parish and county boundaries have changed over the last 500 years.

History website Ancestry.co.uk said its atlas and index of parish registers contains 57 separate county maps, including information on local parish towns and churches.

The maps, digitised from original documents held by the Institute of Heraldic and Genealogical Studies, give an insight into how England's historical county maps remained unchanged for centuries before many of the ancient counties were split up to make more governable areas.

Although it does not exist as a county today, Middlesex is shown as it was in the 19th century, occupying large swathes of London such as Islington and Chelsea, while the home counties feature in their original form before the London Government Act 1965 saw the creation of Greater London.

Other counties that appear in the atlas but no longer exist today include Westmorland (now part of Cumbria) and Huntingdonshire, which became a part of Cambridgeshire following a Government Act in 1971. Lancashire is also shown in its original form, comprising modern-day Manchester and Liverpool, as well as parts of Cumbria and Cheshire.

Ancestry.co.uk senior content manager Miriam Silverman said: "The borders of the UK parishes and counties have changed so much over the last 500 years and that really makes these maps the key to navigating the past and progressing with your family history journey."