Known as The Hidden Abbey Project and spearheaded by local historians, the scheme aims to locate once and for all the final burial place of William the Conqueror’s youngest son.

It is commonly believed the monarch and founder of Reading Abbey is buried beneath the now vacant prison but in mixed communications from English Heritage the group has both supported and abandoned the project.

In a letter addressed to Reading Borough Council’s deputy leader Cllr Tony Page, Dr Andrew Brown from the heritage charity offered to undertake geo-physical surveys to start the hunt for Henry I.

But five days later on March 18 an email sent to Cllr Page said it is “unlikely” the group would get involved in the programme after all.

Cllr Page said in a reply: “May I ask what happened in five days to remove the national importance of this site? I am very disappointed that English Heritage seems to be sending contradictory messages.”

For any work to begin on locating the king’s remains, excavations would be needed at the Grade II listed prison as well as other neighbouring sites including St James’s Church, the Abbey Ruins themselves and Forbury Gardens.

Cllr Page said: “There is a long way to go before any physical work can be undertaken around the Forbury or the prison because the future use of the prison obviously impacts on the timetable.

“Until the proposals are clarified for moving forward the future of the prison site there will not be any archeological digs around that area. No responsible authority would give permission for work until we have got a much better idea of what lies underneath the ground — and that requires a serious element of research.”

The prison is owned by the Ministry of Justice, which has come under fire from the council for failing to find a new use for the site since it closed in November 2013.

An outline development framework which would ensure future developers are made aware of the cultural and historical importance of the site is set for approval by councillors this week.