Archaeologists have called for a halt to church redevelopment plans on the site of Ilkley’s Roman fort until an excavation has taken place.

West Yorkshire Archaeology Advisory Service (WYAAS) is asking Bradford Council to defer its decision on plans for a link building between the historic All Saints Parish Church and nearby Church House.

The proposed development is situated within the remains of Olicana Roman Fort, say archaeologists, which is thought to have been built by Agricola in AD70 to 80.

Excavations of the site last century concentrated on the northern section of the fort, but it is believed the ancient Roman headquarters, or “principia”, of the fort is in the southern part of the site, in the church and graveyard area.

WYAAS, the district’s official professional advisor on the historic environment, believes excavation also has the potential to uncover Anglo-Saxon, medieval and post-medieval remains.

It is asking Bradford Council to seek an evaluation of the full archaeological implications of the proposed development.

This would involve the excavation of several evaluation trenches.

A WYAAS spokesman said: “We recommend that the evaluation be carried out pre-determination because further archaeological work to mitigate the impact of the development may be required and a pre-determination evaluation will enable the applicant to take account of the full archaeological implications, in terms of cost and programme, of the project.”

Subsequent advice would depend on the result of the evaluation, says the service.

It is also asking for Saxon crosses to remain in situ and for the submission of further information, including an artist impression in colour, illustrating the elevation of the proposed link building as seen from the church.

The current plans suggest a watching brief for archaeological features during groundworks for the link building, but WYAAS feels this is not appropriate, with Roman remains of “national significance” on site.

All Saints wants to make its facilities accessible and up-to-date for today’s community needs. The cost of the project, which includes internal alterations of the buildings, is expected to be £700,000 or more.

Christian worship on the site is thought to date back to the 7th century AD, and the first church there may have been built using stone taken from the abandoned Roman fort. Much of the exterior of today’s church dates to the late 1800s, but the tower and other features date back to medieval times.