The visit coincided with the 363rd Anniversary of the Battle of Naseby. Members said they heard clunking noises as well as sounds like cannonball fire.
When the group then looked through pictures they took
during the visit, they spotted what appeared to be a mysterious figure walking
out of the dark
carrying something in it's hands.
Emma Whiteman, leader of the group, said: "The picture
was taken about an hour after we heard the noises but we didn't see anything at
When we saw it, when we were looking back through the pictures, we were gobsmacked.
We are saying that it's a soldier. Some people can see it sitting on a horse and some people just see it as a walking soldier."
The Battle of Naseby in 1645 was a key win for the Parliamentarians over the Royalists in the English Civil War.
The battle involved more than 21,000 troops when the Royal army, under Prince Rupert, was beaten by Parliamentary troops led by Sir Thomas Fairfax.
Adrian Perkin, an author and 'ghost detective', said he "thought the image was a soldier with a musket or pike walking through a gateway."
He said: "If this is genuine it's a very, very, good example. It's the best I have seen for many years."
Sceptics said the effect was caused by the camera itself.
Anne Haddon, of The Naseby Battlefield Project, said: "I
haven't heard anything like this at the battlefield in all my association with
It's fair to say I am a bit sceptical."